First things first: There are no custom player character portraits
in FRUA, only custom player character (combat) icons
Importing player character icons transcends the scope of a French vanilla design; it's not an option the original FRUA offered, so it can only be done by hacking. It's highly recommended to have UAShell installed in order to deal with CBODY.TLB hacks. Like the name says, UAShell is primarily a shell, not a hacking tool, but it manages all kinds of hacks without messing up your original files, and it allows you to start several hacking tools via its menus.
The hacking tool you're looking for is probably CBEDIT by Dan Autery. It should be included in an UAShell installation (run it from the menu: Editors/Other/CBODY.MNW/CBODEDIT.MNY), but you can also download it separately from the UA archive
(cbedit.zip). I have worked with it in the past, but to give detailed instructions on how to use it, I'd have to familiarize myself with it again. It's not really hard to understand, just a bit roundabout. I think it will ask you for the number of the slot you want to replace (0-48?) and then for the pcx file it should import your character icons from. Then it will write the changes to a new CBODY.TLB file. If you have UAShell installed, applying the hack is as easy as dropping the new CBODY.TLB file into the folder of the design you're working on and running it via UAShell.
In any case, if you plan on creating your own designs, using hacking tools, or even creating your own hacking tools, I also highly recommend joining the FRUA community forums at ua.reonis.com
. They're a very friendly bunch and much more knowledgeable about any of these things than almost all of the GOG community members. I'm active in both communities, but my knowledge has limits.