This is a good question, and for FIS the simple answer is probably, but it is not as simple as that. Furthermore, this is just my interpretation, as I am not speaking for the FIS (at least not in this capacity). Just as you can modify homologated flex poles with parts from various manufacturers, as long as the parts all homologated, you should be able to do this.
However, because the wand itself, works in conjunction with the switch, it may change the point (measured angle) of opening of the actual switch. Alge may assume on amount of flex from their wand and set their switches accordingly to open within the allowed tolerance, and Tag builds their wands to flex so as to open their gates and trigger their switches at a different spot. If changing the wand allows the switch to trigger outside of the allowed range, you certainly have a problem.
My feeling is that you should never switch types mid run, however between races might be ok, but not advisable.
Attached is the specification found here:
http://www.fis-ski.com/data/document/timingbooklet-v2_42.pdfThis is the current version of the FIS Timing Booklet (2.42)
Jenna