Infanttry icon numbers are hard coded. That means you cannot change the look of your squad with MOBhack. Same with all infantry units, only crew-served weapons (howitzers, mortars, flak, mrls...) can be modified.
However, if you open the right .shp files with SHPed (icon0010.shp thru icon0015.shp IIRC) you will find the inf squad icons for the various crew numbers. There are several colors following country, but which country uses which colors IS hardcoded and unmoveable. Now if you feel like it and have a precise idea in mind, you can extract these infantry icons, edit the images and replace them in the files.
At least I guess you can. I never tried this but it doesn't sound too buggy, provided you do everything quite right.
Same with the sounds. Not much hardcoding that you can't bypass.
Go in the Data\Sounds folder or something like that, you'll find all the sound files (.mp3) and the .ini list saying what sound is what and (important) what
filename refers to what sound reference number used in MOBhack. By cross-referencing both you can change any unit move or weapon sound for any in the database. And add or replace with your own ones
Have fun!