Alexandra has called my attention to the following comprehensive review of laws and practices around the registration of foreign travellers to Russia:
Another version of the same is at ru.wikibooks.org. Both in Russian 🙁
I’ll be flipping through what seemed at a glance to be a serious piece of work, especially if you travellers continue asking me to do registrations for you here in Kandalaksha.
Yes, I can still do them here but only to my Moscow address. That will suffice for most purposes.
..PS. Checked with the Post Office here in Kandalaksha. Yes, doable. Still the same fee of $50.