I did a Google search indeed. There is not much to find on this topic, but the most easy solution seemed to send all my black bytes to a wallet on another device, wait until confirmed and send everything back to the 'linked address'. Black bytes payments carry a payment fee in 'bytes', I think, but about 2,000-3,000
bytes per payment is negligible.
For the 'bytes' in my wallet: the explorer indicates that they have indeed moved to another 'change' address so the 'linked address' shows a balance of zero in the explorer. But for bytes that should not matter in respect of the airdrop; only the black bytes must really be in the 'linked address'.
[edit]: apparently, moving black bytes around makes no sense as they apparently do not count for the 20% bonus, but the 'bytes' must be in a linked address to be eligible for the 'black bytes' bonus.
BTC to bytes: 1 BTC of proven balance gives you 62.5 MB (0.0625 GB)
BTC to blackbytes: 1 BTC of proven balance gives you 2.1111 * 62.5 million blackbytes (money supply of blackbytes is 2.1111 times more than that of bytes)
Bytes to bytes: 1 byte on any Byteball address gives you 0.2 new bytes
Bytes to blackbytes: 1 byte on linked Byteball address gives you 0.42222 blackbytes
Just followed up on the advice to move all 'bytes' to the main address again via the transition bot. Slow learner here...
Thanks for all the help.