legal source confirming non OY- EASA reg aircraft can’t be based in DK, preferably a link to a danish government entity would be nice.
While I’m no expert on this subject I quickly found some documents under “trafikstyrelsen” which includes Danish CAA. I think it depends on the situation.
In there is a section about right and obligation to put on an aircraft on danish OY-reg. If your resident in Denmark (either as individual or company) and its private flying then as rule your obligated to put the aircraft on OY-reg. If its commercial flying on a danish AOC then it’s also an obligation to put the aircraft on danish OY-reg.
If you are not resident in Denmark you may have a rights to have/keep an aircraft on OY-reg, if your in EU, Island or Norway and have some connection to Denmark. They don’t write what that connect could be and is evaluated from case to case.
I can’t find any info on the case if an EASA-reg (non-OY) aircraft operated by somebody not resident in Denmark want to base it in Denmark, but that’s probably not a likely scenario anyway.