When I send from an HD address, how does Mycelium select which addresses to send from?
Actually I would like to know whether I can influence which address is used by choosing a particular amount to transmit. For example, if I choose to send the exact amount of one of my addresses, will Mycelium then empty that address? How about the fee in this scenario? This would amount to some kind of indirect coin control. Would be nice to have.
HCP explained why that would be hard to do, with Mycelium lacking coin control
I think if you want to empty a particular address in your HD wallet, you should get the private key of that address and import it into a different wallet: a single-address wallet, not HD. Then you can send the coins from that address and that address alone. You could try using a Mycelium legacy address. It would probably work.
I haven't done it, so I'm not sure what's the easiest way to get the private key from an address in the Mycelium HD. If Mycelium HD doesn't show the private keys of individual HD addresses, then you will have to use an external utility that generates series of HD addresses from seed.
Here's an example of such a uility:
https://iancoleman.github.io/bip39/of course, you can't do that online with any expectation of safety, so you would have to save the web page and run it offline, or better yet download the code from github and check the pgp signature.
It's been a long time since I fiddled with this stuff. I seem to remember there are two kinds of address in the HD wallet, receive addresses (which receive external funds) versus "change" addresses, in which you receive funds from yourself.