Hi,
what do you mean by editing the terrain (you can not change the terrain of Google Earth directly). What you describe looks to me like two problems.

1. You get model rejections (from reviewers) that you don't want to get. If you just use Building Maker to model a building that you want to use yourself for a design, but don't want to submit it to Google Earth, you can also set it "not ready for Google Earth". You find this on the model details page in 3D Warehouse by clicking edit → edit details. Unfortunately Building Maker models are by default submitted immediately into the review queue, not even with an option to save as a draft.

2. In SketchUp itself (not in Building Maker) you can import a snapshot of the area and terrain. This terrain is locked. While it would be editable after unlocking, it doesn't affect the Google Earth terrain. If you don't intend your model for Google Earth you can just edit it without worrying, but if you want to add changes for the Google Earth terrain, you would better create your own additional terrain on top of it. For example if the building sits in reality higher, you would add a "terrain skirt". If the building sits deeper, you can not dig into the Google Earth terrain, so you would raise a terrain skirt up and add a depression in the center.
See here for an idea: https://sites.google.com/site/sketchupsage/google-earth#TOC-Create-Artificial-Terrain