MW3 Customizing Map list/gametypes

[Stray Cat]

Easiest way I found to create custom map list is to edit the default.dspl file. As an example:
mp_exchange,TDM_default,1
mp_hardhat,KC_default,1
mp_interchange,TDM_default,1
mp_lambeth,KC_default,1
mp_mogadishu,TDM_default,1
mp_plaza2,GG_default,1
mp_radar,TDM_default,1
mp_seatown,KC_default,1
mp_underground,TDM_default,1
mp_village,KC_default,1
mp_paris,TDM_default,1
mp_alpha,GG_default,1
mp_bootleg,TDM_default,1
mp_bravo,KC_default,1
mp_carbon,TDM_default,1
mp_dome,GG_default,1

See default.dspl for valid map names and gametype (dsr files)

As per default.dspl
//format is
//<mapname>, <dsr filename>, <weight>

NOTE: There is a misspelling in default.dspl file: mp_labmeth should be mp_lambeth

As for game type (dsr files); these hold a lot of details. Every dsr file contains specific choices that are relevant to that gametype only. The files also contain duplicate details on all the other options that apply to all gametypes. This is to allow you to customize a specific gametype. You can allow a killstreak, perk or weapon to be used in one gametype but not another.
Example: no laststand or as it is now called finalstand,
0 means it is allowed , 1 means it isn`t
gameOpt commonOption.perkRestricted.specialty_finalstand "0" // [ 0, 1 ]

Some features for hardcore & non-hardcore are coded into the iwd or exe files, not sure which. If you choose hardcore you can not set respawn time. It defaults to 10 secs. In hardcore there is no minimap and you can't turn it on. In non-hardcore minimap is on and I haven't found a way to turn it off.

[Stray Cat]

One important thing I forgot: if using NFO control panel to modify files, Stop your server while making any changes. Once finished start server. Good habit to get into is backup the file you are amending before you make the change. And don't forget save the file after you make the change.
This is the order I tend to follow when making any mods:
Stop server
choose file I am going to amend
Copy or download the file
Edit the file
Save
Start server
Check to make sure server is running
Ensure players can connect by joining your server.
Recommendation: modify only one file at a time. make only one or two changes at a time.
If you decide to use ftp and download the file to modify; DON'T USE WORD!! as your editor, use notepad or notepad++
You will need to re-start your server after you make any mods to any file.