Is it allowed, without that bad things happen, to change Union ACTION, CREATE, SEARCH policy, after some days usuage? (data is written to the remotes in this union) Would a change mess up everything?
What is your rclone version (output from rclone version)
rclone v1.52.2
os/arch: linux/amd64
go version: go1.14.4
Which OS you are using and how many bits (eg Windows 7, 64 bit)
Debian 10 - X64
Which cloud storage system are you using? (eg Google Drive)
GDrive
The command you were trying to run (eg rclone copy /tmp remote:tmp)
If you have files you already uploaded, you'd see them on one of the remotes. If you are using epmfs, it would have written to the remote with the remote free space while that was active.
If you are using eprand, it would be a random remote in the union.
Changing it just changes the new uploads that are written and anything that was already there, is already on the remote it is at.