I have butt implants (not gluteal) & 2nd BBL in few days - is it dangerous to undergo?

If gluteal implants are not placed correctly and have this is both edges or show during certain positions then you need a revision of your implants not a BBL.
That transfer is usually not effective at hiding the edges of gluteal implants that were placed incorrectly above the muscle.
Gluteal implants have high complication and high failure rates. failure can be a bit of a loose term since for some people dissatisfaction with the procedure eventually is sufficient for individuals to have the implants removed making them a failure.
You already had a BBL so it shouldn’t be much difference for the second one though I suppose perhaps you had the implants after your first BBL.
Your situation is a bit complex and without pictures we can’t make an assessment.
Delivering consistent quality liposuction and fat transfer results is more difficult than most people believe. There is substantial differences in outcomes, skills and experience depending who you choose for your procedure.
For that reason I recommend patients be very selective in choosing providers for liposuction and fat transfer procedures.
If you have issues with your implants then perhaps the next procedure should be one that deals with the problem directly.
In general I recommend patients have multiple in person consultations avoiding virtual consultations whenever possible. I also recommend avoiding traveling long distances for elective procedures whenever possible.The exception is finding specialists who have true specialization and gluteal implants. They simply are not a lot of plastic surgeons you have enough experience to do videos of plans correctly with consistent long-term success and for that procedure you may need to travel.
Good luck,
Mats Hagstrom MD