Hey nehebka
To mod your login screen, you will need to edit the "LOGINBG.dtx" file located in ("C:\Nexon\Combat Arms\Game\UI_SCR_LOADING.rez\LOGIN\LOGINBG.dtx")
Convert it to LithTech and edit it. Then convert it back to Nexon. Then inject it back into "UI_SCR_LOADING.rez"
Or, you can just make a picture of your own in Photoshop or GIMP and save it as a DTX file and just put it in the path above. But always make sure to make a backup copy of the file you edit before ever touching it!
Here's my
Login Screen if you want to see it.