NOTE:These 4 levels arn't require a download (they are built in the game, just hidden), but the other 20 levels are in a modpack.

There are four hidden levels in Edge which are totally playable, they are scientist, switchboard, islands & tide.
Just add following XML into levels/mapping.xml before </bonus>and you can play these levels:

<level filename="scientist_803" leaderboard_id="46020" name_sfx="scientist" />
<level filename="switchboard_807" leaderboard_id="46022" name_sfx="switchboard" />
<level filename="islands_809" leaderboard_id="46018" name_sfx="islands" />
<level filename="tide_814" leaderboard_id="46023" name_sfx="tide" />

The file place in steam folder:
C:\Program Files (x86)\Steam\steamapps\common\EDGE\levels
The folder that you installed steam in it (The path is not have to be like the path that steam installed in my computer).

You can reach it by:
Right click on Steam shortcut -> Properties -> Open file location.
Than you need to continue enter that path: \steamapps\common\EDGE\levels

1. Find the file mapping.xml in Edge directory
(Right click on Edge->Properties->Local Files->Browse Local Files->Levels folder
Or from your Steam directory: \steamapps\common\EDGE\levels)
2.Open as notepad
3. Find the bonus end tag (this: </bonus>)
Tip: You can use CTRL+F to find the tag.
4. Paste before him:

<level filename="scientist_803" leaderboard_id="46020" name_sfx="scientist" />
<level filename="switchboard_807" leaderboard_id="46022" name_sfx="switchboard" />
<level filename="islands_809" leaderboard_id="46018" name_sfx="islands" />
<level filename="tide_814" leaderboard_id="46023" name_sfx="tide" />

Save the file and enjoy!

Video of me doing it in my computer (4 levels) :

Edge tool download (Chinese & English) : https://github.com/Mygod/EDGE/releases

EdgeTool requirements: Microsoft .NET Framework 4.5.1

Mods:
WEGFan's Achievment Map[www.dropbox.com]
Edge Mods Site: Replace the "index.html" in "edge/expanding-edge/download-edgemod/top-download.html".

Instructions

1.First you need to make sure that Hide extensions for known file types is disabled
Go to: Control Panel->Appearance and Personalization->Folder Options->View->Uncheck the box "Hide extensions for known file types"
2. Download the mod/Levels

If it is mod:
3. Change the type of the file to RAR/ZIP (Change the .Edgemod to .Rar/.Zip)
4. Open it
5. Coppy every file in each folder to the appropriate folder in Edge folder
(Right click on Edge->Properties->Local Files->Browse Local Files
Or from your Steam directory: \steamapps\common\EDGE)

If it is level/s:
3. Change the type of the file to RAR/ZIP (Change the .Edgemod to .Rar/.Zip)
4. Open it
5. Coppy every file in each folder to the appropriate folder in Edge folder
(Right click on Edge->Properties->Local Files->Browse Local Files->Levels folder
Or from your Steam directory: \steamapps\common\EDGE)
6. Open the mod.xml file as notepad and coppy every line that start with "<level" to your mapping.xml notepad before the </bonus> tag
(Right click on Edge->Properties->Local Files->Browse Local Files->"Levels" folder
Or from your Steam directory: \steamapps\common\EDGE\levels)

In this example the file is arleady in Zip type. In other cases you will need to convert it to Zip/Rar.
If you dont know how look at "How to install Mod/Level sector.

1.Download the EPIC Edge modpack:
Download Link[www.dropbox.com]
(you should enter the index file in the mirror files and replace the "index.html" in "edge/expanding-edge/download-edgemod)
2. Go for Edge directory:
(from your steam folder your steam folder \steamapps\common\EDGE\)
or
Right click on Edge->Properties->Local Files->Browse Local Files->Levels folder
3.Copy the files in "audio", "levels", "models", "music" separately into the game's "audio", "levels", "models", "music" folder.
4.Find the file mapping.xml in Edge directory
(Right click on Edge->Properties->Local Files->Browse Local Files->Levels folder
Or from your Steam directory: \steamapps\common\EDGE\levels)
5.Open as notepad
6. Find the bonus end tag (this: </bonus>)
Tip: You can use CTRL+F to find the tag.
7. Paste before the tag the content of the "mod.xml" file in the mod (It might be in the levels folder).

In that mod the content of the "mod.xml" file is:

<!-- Android Extended Level 10 -->
<level filename="level556" leaderboard_id="70556" name_sfx="minicube"/>
<!-- Android Extended Level 12 -->
<level filename="level555" leaderboard_id="70555" name_sfx="furious_bot"/>
<!-- Android Extended Level 14 -->
<level filename="level557" leaderboard_id="70557" name_sfx="vertical_way"/>
<!-- Android Extended Level 19 -->
<level filename="level558" leaderboard_id="70558" name_sfx="cargo"/>

<!-- Android Extended Bonus Levels x15 -->
<level filename="level574" leaderboard_id="70574" name_sfx="crystal_mine" />
<level filename="level570" leaderboard_id="70570" name_sfx="remember" />
<level filename="level572" leaderboard_id="70572" name_sfx="zero" />
<level filename="level560" leaderboard_id="70560" name_sfx="the_wall" />
<level filename="level563" leaderboard_id="70563" name_sfx="rush" />
<level filename="level564" leaderboard_id="70564" name_sfx="cubing_machine" />
<level filename="level561" leaderboard_id="70561" name_sfx="the_wall_2" />
<level filename="level567" leaderboard_id="70567" name_sfx="black_way" />
<level filename="level568" leaderboard_id="70568" name_sfx="curious_land" />
<level filename="level562" leaderboard_id="70562" name_sfx="the_wall_3" />
<level filename="level575" leaderboard_id="70575" name_sfx="little_seed" />
<level filename="level569" leaderboard_id="70569" name_sfx="space_noise" />
<level filename="level571" leaderboard_id="70571" name_sfx="magic_maze" />
<level filename="level566" leaderboard_id="70566" name_sfx="piano" />
<level filename="level573" leaderboard_id="70573" name_sfx="star_heart" />

<!-- AWESOME PIRATES SPECIAL OFFER! x1 -->
<level filename="level554" leaderboard_id="70554" name_sfx="path_of_piracy"/>

Save the file and enjoy!

Video of me doing it in my computer (20 levels) :

How your Edge need to look if you done it correctly: