Those heat pen things look like they are worth a shot for sure ,
I got some dye from america , I had some success but even your an expert its a slow process , most of the time I woundnt be able to charge for it or have the time to do it , and it only works on wool and possibly nylon .
The pics I posted, can't see them on my phone now ... But the bottom green carpet was a boutique hotel ,40 rooms , they get a young clientele who bring cocktails etc to the rooms. About 5 stains per room , not cost effective to bleach dye each stain ...but the paint was very quick and good enough to get a result .