User role: modifying a screen for certain users only

If I have to modify a screen (e.g. VA21) and I want the changes to be applied to some users only (those with a certain role), is the unique solution to test in my script if Q[Role=xxx] or is it possible to activate GuiXT for a particular group of users only?

You can also use the "user catalog" to activate GuiXT for certain user roles only.
Here is an example:

Normal user catalog entries:

// User groups:
// make correspondance to 1-4 script directories
M1 \\P5008\GuiXT\General \\P5008\GuiXT\M1
M2 \\P5008\GuiXT\General \\P5008\GuiXT\M2
MX \\P5008\GuiXT\General
TEST \\P5008\Guixt\Test
XX none

// User:
// make correspondance to one user group

000/Adam          M1
000/Rinaldini     M2
000/Zeno          M1
000/*             MX // other users in client 000

800/Anton         M1
800/Bertini       M1
800/Cemicz        M2
800/Smythe        M1
800/Mueller       M2
800/Zencke        TEST

* XX // other users, all clients

// Alternative:

// role or profile specific settings with
// Role=.... or Profile=...
// (valid for all clients)

Role=SAP_FI*            M2