You can make main characters from different saves as companions, pretty easily...
Put your main character in third person mode so you are behind him or her.
Get into the console mode.
Click on your character; his/her name should show up at top of screen.
Type in
createfullactorcopy
Hit ENTER button
Get out of console mode.
Like, WOW...You should now have a duplicate of your character standing near your origional character!
You can use the Companion Share and Recruit mod to make him/her a companion.
BUT I usually save the game first, get into Wrye Bash, and copy a new face onto my main character by going into Wrybash's list of Oblivion saves, right clicking onto the save I am on, then choosing the copy face command option that appears on a drop down list after right clicking an my save. The rest is easy.

All of these characters are from one main character, who's faces, sex, hair have been changed in Wrye Bash, then made into companions by a companion mod. Probably the face on the left is the origional face; the two in the rear are companions. Quentin Tarantino (front) is now the main character.
Wrye Bash takes some work to get it working, since you must install Python software also, but it is worth it.

An interesting note is you don't need to pay for anything to do this if you are not making celebrity faces using SI Facegen. You can use stock Facegen faces from other main characters you may have created. So come to think of it you don't even need to go into Construction Set to do this...