Had Upper/Lower Blepharoplasty 3 Wks Ago, Can I Dye My Lashes?

Yes, the skin healing has likely been completed by now and dyeing the lashes should not be an issue. But your surgeon has the last say on these matters. Run it by him/her before you do it.

Although the normal healing time for upper/lower blepharoplasty about 1-2 weeks has passed, I suggest asking your cosmetic eyelid surgeon as you don't want to risk complications.

In my office, it would be no problem.  However, different surgeons have different feelings about the timing of this.  For this reason, you need to seek the advise of the surgeon who knows your eyelids the best.