To be honest i have to say that i didn't play around with the ingame look so much.
Maybe it's not a picture in the background, maybe it's a bink video.
But to say that, i would need the mod to see the structure.
For me it would be the easiest when you give me the downloadlinks from the mod from what you want to use the look and from the mod where you want to change it.
With that i could give you exact instructions what to change.
But you can try this before by yourself:
The following lines in the *.rfm are the interesting ones for a part of the look of the menu and other looks:
OptionsAnim=
OptionsSounds=
OSCFile=
OptionsDir=
If they are deactivated (means that they have 2 slashes (//) in front, there is no customized look for the mod.
But if they have special entries, you have to change the content of the defined folders, to get the wanted look.
Now look into the *.rfm file of the mod from what you want to change the look and there at the lines i've listed above:
OptionsAnim=
OptionsSounds=
OSCFile=
OptionsDir=
Look at all lines that don't have // in front and look what stands behind the "=".
You will get 3 foldernames and 1 filename.
To get backups, copy all defined folders into an new one that you call "modxxxx_UIBackup" for example.
The OSCFile normally is in the OptionsDir-folder, so you don't need to backup it seperately.
And the OptionsAnim and OptionsSounds -folders normally are included in the OptionsDir-folder too.
Delete all the content of the folders.
Now copy the content of the similar folders of the mod you want to use the look from, into the empty folders and rename the OSCFile as it is set in the *.rfm file.
That is a bit complicated, i know, but i would suggest to do it that way, because if you choose the easier way and edit the *.rfm-file, you'll get mismatches online.