If I already have a chin implant, is it safe to get lipo?

Liposuction in the submental area under the chin should not be affected by prior placement of a chin implant. The implant is typically placed along the lower border of the jaw, and the small incision that is created for liposuction is typically well below/behind this. There are several issues that can cause the appearance of a double chin, and liposuction is only one treatment alternative. I would recommend seeing a plastic surgeon who specializes in facial aesthetics to evaluate whether this would be the best option for you.
Best wishes,

It would be fine to have liposuction under the chin with a chin implant in place.  The puncture for the liposuction is normally made just underneath the chin and below the chin implant.