I'm not sure if you want to replace the weapon or replace the msh of the weapon. I'm going to assume msh. (Try to be more specific next time you have any questions, it helps us help you.
1. Munge a map. (If you need help with that just let us know)
2. Copy over the CIS asset from C:\BF2_ModTools\assets\sides
3. Paste the copied side in C:\BF2_ModTools\data_ABC\Sides
4. Open up the cis side folder and open up the odf
5. Search for the file named cis_weap_inf_pistol.odf
and open it
6. Inside you will see the lines
7. Replace "cis_weap_pistol.msh with "cis_weap_inf_rifle.msh
8. Replace "cis_weap_pistol with" "cis_weap_inf_rifle.msh"
9. Replace "cis_1st_weap_inf_pistol" with "cis_1st_weap_inf_rifle"
10. Go to C:\BF2_ModTools\data_ABC\_BUILD
11. Go to Star Wars Battlefront II\GameData\DATA\_LVL_PC\SIDE and back up cis.lvl and cisshell.lvl
12. After munging go to C:\BF2_ModTools\data_ABC\_LVL_PC\SIDE and copy cis.lvl and cisshell.lvl
13. Paste cis.lvl and cisshell.lvl in Battlefront II\GameData\DATA\_LVL_PC\SIDE
14. Run the game and enjoy your changes!
Make sure to look around the forums as well, get to know where everything is. In the modding topic there is a FAQ on the top of the page that lists all the tutorials on the forums. It can be of great help. "résolu"means "Resolved" and "unrésolu" means Unresolved. Oh, Welcome to the forums!