Is there a way on NFactor Flow to add a suffix to ${AAA.USER.NAME} on a PrefilUserFromExpr login schema? So that user becomes, for example, user-internal.

Your original username would be sth like

abc123

and then you would like to add a suffix like

@domain.dom

to it resulting with

abc@domain.dom

?

Affirmative, I try to modify what is sent back

likely you need to just replace the

${AAA.USER.NAME}

with sth like

"domain/\" + ${AAA.USER.NAME}

... not 100% on the escape character before the backslash, but the bit in front of the variable is just a static string. It could be that you need to generate the whole variable somewhere, but you get the idea