How does upgrading and downgrading Velocity status and Hilton HHonors / Europcar Privilege work?

I recently upgraded to velocity gold and so I understand I can activate for a year, gold status for Hilton and Europcar after which you need to maintain with each program and not velocity. I’ve searched online and found some info regarding this and I have read that if towards the end of the year I upgraded to platinum, would these benefits reset?, ie. you would get diamond hilton (6 months but then do the stays to extend it to a year) and europcar elite for another year?

Then what if in the next year you were downgraded to velocity gold could you apply again to Hilton and Europcar (and get gold hilton and europcar executive) as a ‘new enrollment’ as your tier had changed?

I have read that if you the situation was that you were downgraded to silver and then went back up to velocity gold then in this situation it would start anew and you could get hilton gold and europcar again.

Anyone could clarify? Just wondering if it would be worthwhile timing your earning for status credits to drop to silver or lower and then go back to gold in order to maintain the hilton status as for myself I find that more of the benefit than the lounge.