Can I use Velcro for attaching mezuzot?
Yes, this is fine, though it is better to use nails or strong double-sided tape.
Velcro seems to be better than scotch tape, because Velcro is often more “permanent” than scotch tape.
Poskim write in general that scotch tape can be used, provided it will hold for a reasonable time (at least 30 days), but that it is not the preferred way to attach the mezuzah because essentially it is non-permanent. Velcro that is fixed strongly and will not fall off even after a long time is therefore better.
See Kevias Mezuzah Kehilchasa p. 185 for sources on this matter.