2005, OnStar Removel?
 

I have a 05 with the Onstar module and was wondering. Can I remove it? What impact will it have, and are there any switch panels I can replace it with? (For extra lights)

Yes you can but first the only way to completely eliminate OnStar is to physically disconnect the module from your vehicle.
Other than the OnStar system and it’s related services (auto crash response and emergency services) no other system in the vehicle should stop workin when you disconnect the module.

All Onstar modules for the Hummers 03-09 are no longer active due to the decommissioning of 2G/3G cellular. So technically they don't work right now. Lights are on but no one home. You can leave or remove.

On Etsy there is a seller that will let you replace with a blank, or a pocket... I think it is the perfect spot for a switch plate to control exterior lights... but have not seen someone post those yet.

https://www.etsy.com/listing/921313654/
https://www.etsy.com/listing/924390532/

So if I remove the dash part, nothing will be affected? Or are there other parts to worry about?

i believe the dash part is just the buttons and the main module lives further back. at least in my 03 it looked that way.