HPF and OHMS

I've got a little pole up pub system, 15 and 12 with Fane HF250.
It is used 2 way, with an active xover and the HF250's are pasiive HIGH PASS only at 7k.
The 15's are 4ohms and I want to change the 12's for 4 ohms to drag as much power from the little amps. So heres the bit I don't understand:

The HF250's are 8ohms, the HPF is 8 ohms. I know it will do something incorrect to the slope etc but as it's just a little system I'm not too worried. Thing is am I going to damage the HF250's? Thanks to all.

so, as i understand it, you want to change the 12" driver for a 4 ohm driver, but leave the hf250 and high pass filter as is

if that is what you intend to do, you wont have any problems with the hf250 - if anything it will be safer as more of the current will be pulled by the 12" in relation to the tweeter. this will also cause a change in the spectral balance, so you will need to re-eq the system

providing the load seen by the hpf does not change, the x over frequency will remain unchanged
if the crossover is connected to the 12" as well, then that may well cause problems

Many thanks. That is what I presumed , ie an 8r and 4r driver in the same cab, 4r gets more, just wasn't sure how the hpf changed things.
Ta lots
Nick

If there is no passive lowpass to the 12", then your good.