2238's source is how the server was before pre-wipe madness in 2013, and it was said that previous versions of 2238 wouldn't be released.
The access to the original repository used for the development of FOnline: 2238 in the past, with all the revisions up to this point, will stay closed.
As for Perception, changing line 61 in
client_fov.fos looks promising, but I can't test out the code right now, and I think that is just client side. In
main.fos, line 2834 has a FovCheck(Critter& cr, Critter& opponent) function that looks like it would help you. To figure out what makes it change based on what direction your character is facing, you might have to do more searching & modifying.
On Notepad++ for instance, you do do 'Search -> Find in Files..." to find all instances of a keyword like "perception", "fov", "direction", etc.