Yes.

The clear lacquer can be over-coated
at any time. Just make sure it's fully degreased.

Yes

Is it all Halfords standard paint/primer or wheel paint that's being used? If so they are all acrylic so they are 100% compatible with each other.
If its another brand of paint it may not be compatible, particularly if its an alkyd of some type.
How many coats of primer and black have been used?
How long was left between each coat?
If lots of very thick coats have been applied it could be a case of solvent entrapment but this tends to cause pin-holing rather than wrinkling.

This application for Halfords Clear Lacquer This is not what this product has been designed for. Therefore we are unable to comment on it's suitability for this proposed use.
We recommend to contact perhaps a Marine specialist?

Yes - to remove the laquer runs you will need to rub down carefully with a fine grade wet and dry paper - be careful not to damage the pearlescent paint.
Laquer will take several days to fully cure - do not spray in damp or wet conditions - dry and warm conditions are best.

It might not be the best thing to use but it would probably work fine. Just be sure to avoid spraying on the strings or moving parts.

Yes the clear lacquer can be used over gloss for improved gloss,
durability and protection (although its not strictly required). It is
however essential over metallic and pearlescent finishes to ensure the correct colour match and to help protect the aluminium / mica pigments in these paints from the atmosphere. Use either lacquer.

Yes it will work well. Just need to make
sure all traces of polishing agents etc are removed first. Degrease with white spirit and allowing to dry thoroughly.

If you use a clear lacquer top coat the finished surface won't look matt.