If I get the HPF fittings, and remove the capacitor, is there any reason
why it should
not work as a low power factor fitting i.e. not register on the meter.

Both HPF and LPF fittings will register on a normal electric meter. You are
not going to get free electricity by removing the power factor correction.

Correcting the power factor makes the fitting draw the power it needs more
efficiently. A domestic meter can't detect this inefficient use of
electricity, but a commercial meter sometimes can. So a commercial user has
to pay a penalty when they use electricity inefficiently due to power
factor, whilst a domestic user does not.

However, there is no disadvantage to the domestic user (and there is a
slight advantage, in fact) to power factor correction anyway.

Christian.