Can I modify the 70-7551 harness to a 70-7550 harness simply by cutting off the RCA connectors?

I ask b/c I'm about to install a DD unit in our '06 Gx and if I encounter the engine-"whine" or volume issues, I'd like to try the 70-7550 harness... I have a Bose unit in the G, and my DD unit is a 4.0V unit...

Also --

What's the best way to fill the JDM gap? I have a universal scosche trim ring as well as a universal Metra trim ring (oversized) ..
- dremel
- exacto knife?

thanks