A few (hypothetical) suggestions:
1) Don't let a building come between you and your drone, or you will probably lose connection and it will try to Return To Home, which will be tricky at best given all the tall buildings and structures, which leads to my next point:
2) I would set my GO4 APP to "HOVER" instead of "RETURN TO HOME" in case of signal loss. That way, if you do lose connection, the drone will hover in place while you reposition yourself for direct line-of-site to re-establish a connection, rather than relying on the RTH to dodge all obstacles on it's way back to you.
3) I would go into it with the understanding that there's going to be a LOT of interference downtown, so you may have a very weak connection and probably won''t be able to get nearly the distance that you're used to without losing connection.
4) I would try NOT to fly over any pedestrians, so the best time to do it would probably be very early morning on a Saturday or Sunday or sometime when you know downtown won't be busy. Plus, early in the morning will probably give a better lighting scenario for footage, compared to the middle of the day. Downtown Dallas is a ghost-town at sunrise on the weekends.
5) Be VERY wary and careful of the wind gusts in and around the buildings at higher elevations. I'd try to do it on a day when there is VERY little wind, and still, don't get very close to the corners of buildings.
6) Your very best bet, if you can do it, would to be to get on the roof of one of the buildings IN or NEAR downtown. The height advantage will make it easier for you to maintain a visual line-of-site (hence a better connection), and will make it easier for you to have a little privacy and not be bothered by nosey pedestrians. It's easier to get on the roof of many of skyscrapers than you might think. Just take the elevator to the top floor, look for a maintenance door, and/or get in the fire-well/staircase and walk up - assuming that this door is not locked, and they often are.
(You could always ask the building maintenance staff for assistance, but they will probably say NO unless you have a good reason or are a real charmer, and I usually find it easier to ask for forgiveness than permission, as long as I know I'm not breaking a law or endangering anyone. ) There aren't any laws about getting on the roof of a building if it's unlocked, so the most anyone could do is ask you to leave. I've been on the roof of many of the taller buildings in downtown Dallas. Be prepared for possible security cameras on the roof.
P.S. These are just hypothetical points: NOT responsible if you lose/crash your drone or hurt someone. Don't even attempt it unless you have a lot of experience.