First, you'll need the RABCDAsm tool which is available in GitHub: https://github.com/CyberShadow/RABCDAsm
Download the latest release of the tool on a standalone directory.
Open the directory of the tool.
Then open a new window of your file explorer, then navigate to the game folder and drag the Caravaneer2.swf onto the abcexport.exe
This will create Caravaneer2.abc file.
You then need to disassemble the new Caravaneer2.abc file by dragging it onto the rabcdasm.exe and the executive will generate a new folder in RABCDAsm's folder named Caravaneer2-0.
Open the new folder and enter the Data folder.

You then need to modifiy the Presets.class.asasm file by using a text editor (notepad ++ for example).
Attention: for the following two modification, you need to keep the same formating as suggests the context, i.e. all the space.
Search for 1613 and you'll find the section of code corresponding Lintu. Then search for transportAssortment and you'll find the following code:
pushstring "transportAssortment"
pushstring "type"
pushbyte 1
pushstring "amount"
pushbyte 1
newobject 2
pushstring "type"
pushbyte 4
pushstring "amount"
pushbyte 2
newobject 2
newarray 2
Replace it by
pushstring "transportAssortment"
pushstring "type"
pushbyte 1
pushstring "amount"
pushbyte 1
newobject 2
pushstring "type"
pushbyte 4
pushstring "amount"
pushbyte 2
newobject 2
pushstring "type"
pushbyte 13
pushstring "amount"
pushbyte 1
newobject 2
newarray 3
Then proceed to search for pushshort 845 and you'll find the section of code corresponding Autz. Then search for transportAssortment and you'll find the following code:
pushstring "transportAssortment"
pushstring "type"
pushbyte 3
pushstring "amount"
pushbyte 2
newobject 2
pushstring "type"
pushbyte 7
pushstring "amount"
pushbyte 1
newobject 2
pushstring "type"
pushbyte 9
pushstring "amount"
pushbyte 1
newobject 2
pushstring "type"
pushbyte 10
pushstring "amount"
pushbyte 1
newobject 2
pushstring "type"
pushbyte 11
pushstring "amount"
pushbyte 2
newobject 2
pushstring "type"
pushbyte 12
pushstring "amount"
pushbyte 1
newobject 2
pushstring "type"
pushbyte 15
pushstring "amount"
pushbyte 1
newobject 2
newarray 7
Replace it by:
pushstring "transportAssortment"
pushstring "type"
pushbyte 3
pushstring "amount"
pushbyte 2
newobject 2
pushstring "type"
pushbyte 7
pushstring "amount"
pushbyte 1
newobject 2
pushstring "type"
pushbyte 9
pushstring "amount"
pushbyte 1
newobject 2
pushstring "type"
pushbyte 10
pushstring "amount"
pushbyte 1
newobject 2
pushstring "type"
pushbyte 11
pushstring "amount"
pushbyte 2
newobject 2
pushstring "type"
pushbyte 12
pushstring "amount"
pushbyte 1
newobject 2
pushstring "type"
pushbyte 15
pushstring "amount"
pushbyte 1
newobject 2
pushstring "type"
pushbyte 13
pushstring "amount"
pushbyte 1
newobject 2
newarray 8

You then need to assemble the .asasm file back. Within the Caravaneer2-0 folder you'll find the Caravaneer2-0.main.asasm file, you need to drag that file onto the rabcasm.exe found in the directory of the RABCDAsm tool.
A new file named Caravaneer2-0.main.abc will be generated in the Caravaneer2-0 folder, move the generated file into the directory of the RABCDAsm and proceed to the next step.

After that, you'll need to update the .swf file, open the cmd terminal and type:
cd the the directory of the RABCDAsm tool
or if you have installed the RABCDAsm tool on other disk (the D: for example), type
cd d/ the the directory of the RABCDAsm tool
You may finally update the .swf file by typing the following command in the cmd terminal:
abcreplace Caravaneer2.swf 0 Caravaneer2-0.main.abc

And it's done, you can now create a new save and rush to Lintu to test if the Umi Alpha is present on the inventory of the Merchant. If so, you may find Umi Alpha on Autz which can only be unlock on the later stage of the game.

Credit:
This modding guide owes a lot to the Noddite's blog which can be found on the https://caravaneer2.fandom.com/wiki/User_blog:Noddite/Sample_Transport_Modding
I consider all the user blog of Noddite as must-have for modding Caravaneer 2 and I recommend you to read them if you're interested in modding this game.
I also need to thank the contributors of the RABCDAsm tool who make an essential tool for modding flash games.