Can I Believe for Excess Flab and Stretch Marks to Disappear After I Have Lost a Lot of Weight?

First, congratulations for losing enough weight for this to be an issue!  I don’t see any reason why you couldn’t believe for this, as all things are possible to him who believes (Mark 9:23).  At this writing, I don’t know anyone who has believed for this, but I’m not going to use my limited experience as a ceiling for what is possible with God.  I’ve seen Him take care of far more outlandish things than this.

There is no specific Scripture where someone came to Jesus and asked for the disappearance of evidence of weight loss, but I could see this legitimately falling under the category of having God “renew your youth like the eagle’s” (Psalm 103:5).