Dunno if there's a different version for TRS2004, but the PM2IM I have will "convert" IM to IM - in other words if it's already an IM, you can click "convert to IM" after setting the specular color you want, and it overwrites it with the new IM.
You have to toggle "Use specular color" on and off, "Zero specular" is actually a true (0,0,0) black, full specular is true (255,255,255) white.
Right is the original model with zero specular, left is after setting the IM for full specular. For most people that's too bright, which is why people generally do zero speculars when converting from PM to IM. There is another option;
Set the specular to dark or medium gray until you get the amount of shine you want. You can even do weird things like using colored speculars;
Same texture, both engines are black but using colored speculars changes the tone. That's way overdone, but you can use darker shades of colors to do stuff like giving it a rusty patina.
