How lock cell format, but not lock cell contents?

[Gavin]

I'm no boffin on this subject, and I may have this all
wrong, but to me the answer is simple:

Select the cells that will need thier contents changed, go
to Format, Cells and go to the Protection tab (far right).
REMOVE the tick from Locked. Now switch on sheet
protection.

Your cells will be protected against format changes, but
will still allow content changes.

Gavin