Actually, the "RTP" refers to "RGSS-RTP Standard". It is theoretically possible to create new RTPs by creating a folder under Program Files/Common Files/Enterbrain/RGSS/ and setting the appropriate registry key (see the Help file topic "RGSS Specifications"), but I have never seen any other RTPs than "Standard" or "RPGVX".
A single game can use up to three RTPs, two of them would have to be other than "Standard".