Dear Christopher, no, sorry, I haven't got any proper documentation for vedha as "transmute, multiply."  I'm just reporting my sense as a reader of some of these texts over a period of time.  Almost every translation I've ever seen (Skt - English) says "pierce".  But it just doesn't make sense to me.  I'm had a look around to see whether there was another dhātu vidh, but there isn't.

Incidentally, on saṅkramaṇa, it's the word that's used in Ayurveda for contagion.  The concept of contagion is almost completely unknown in Ayurveda, but in those rare cases that it is mentioned, it's sam+kram.  There are good essays by Zysk and Das on this in a book Contagion that I edited with Larry Conrad some years back.

Best,
Dominik