Can Houston tell Melo that he'll be the new starting forward? Or would that be disrespectful to Parsons or Jones too?
Better yet with Smart and Young, the Celtics already have 15 roster spots. How disrespectful for them to be calling free agents when they already have a full roster! It doesn't matter if Bogans, Pressey, Johnson, and Babb are unlikley to return, they're all on the team until they are officially traded or waived.
This is a grown man business, you don't worry about hurt feelings. The Rockets are trying to entice Melo to play there, you don't do that by showing him in a number he'll never wear. "We don't want to offend anybody, so we photoshopped you wearing number 89." Of course why they didn't show him wearing #15 which he'd probably end up choosing anyway is beyond me...
Every major recruit at college probably gets shown a jersey from the school they're visiting with their high school number on it. Doesn't matter if that jersey is already taken, it's just a sales tactic, not a binding agreement to give him that number.