You are looking for a script that already has this feature. You might have to download someones mIRC Script to have this option. Or search such web pages as
www.mircx.org or one of the other web sites where they have a large collection of scripts to choose from. I don't think you will get anyone here to make it for you. But there are plenty of people who are willing to help you design a script and work out the bugs.
Now, It is possible to make a script using Dialogs so when you click on a button it will change the theme to any preset themes you may have setup in the script. Now depending on how you design your dialog box you can add as many custom themes as you want to a script with corrisponding files. Here is a basic script using the commands for preset themes. All you need to do is convert it for use with a dialog box with your own custom files
Backgrounds
.Normal Color {
/background -mx
/background -lx
/background -hx
}
.-
.Blue-purple
..bb/tb-blue {
/background -l $mircdirbackgrounds\02-blue.bmp
/background -h $mircdirbackgrounds\02-blue.bmp
/background -mt $mircdirbackgrounds\06-purple.bmp
}
..reverse {
/background -mt $mircdirbackgrounds\02-blue.bmp
/background -l $mircdirbackgrounds\06-purple.bmp
/background -h $mircdirbackgrounds\06-purple.bmp
}
