Rear brake clunk/hot

[His Dudeness]

Yes you can just undo the banjo but you will need to remove the brake reservoir cap first to relieve the vacuum, don't get any fluid on paintwork if you do wash off with water immediately. While the caliper is off carefully loosen off the two bleed nipples & lightly re-tighten ready for bleeding the caliper later.

There's a vent hole in the reservoir to allow atmospheric pressure in so a vacuum can't form. If the reservoir was fully sealed and there was no vent hole a vacuum would form and it could stop fluid flowing through the system