Plastering crack in ceiling - remove old tape or not ?

Hi guys,

I am cleaning up our granny flat for sale and after finding a crack in the main room ceiling (all Hardiflex - no plaster) I removed the old paper tape join, scraped out all the base compound and re-taped (paper taped) and finished. All good.

I then noticed a hairline crack in the bathroom ceiling. I could just paint over it but I would rather fix it up. I do not want to go through the process again of trying to get all the old base compound out of the join. Question is.... Can I just hit the join with a grinder and get rid of the 'mound' from the previous join and then re-tape and finish or should I pull all of the old base compound out again ?

Or just paint over the crack