Is it possible to create a script on a matchcode by means of GuiXT?
The command "Globaltextchange" in elogon.txt script doesn't seem to work for matchcode; I still find the original field name.

Yes and No. If the F4 help user settings are "Control (amodal)", SAP uses a special control in which the GuiXT text changes have no effect.

If the F4 help user settings are "Dialog (modal)", you can use a GuiXT script. But please observe that the same screen is used by SAP for all matchcodes, and the field names are always the same (dynamic labels). You have to ascertain which matchcode is currently displayed. Example:

if Q[Page=A: Vendors (General)]

  Text F[TabCol1(5)] "Supplier"