If you're annoyed that having to blind-mine Convars values each time you boot up the game over and over again. This might be a good news for you. From now on, the modified Convars can now be carried over: however, it requires your manual operation, and I'm gonna tell you how to do that.
To achieve that, firstly, you should launch your game and start a single campaign with any gamemodes, soon after that, a folder named "dynamicsettings" will be created inside the "ems" folder right under your L4D2 game folder.
Secondly, make a quick view inside the folder and find out what you want to modified; for instance, I'd like to have more reserved ammo to SMG, I'll open "submachine_gun_ammo.txt" with my editor(recommend you use Notepad++), replace 650 with 700, then restart the campaign, grab a SMG, and you will see the reserved ammo is 700 now.