Secondary mirror on a 10" f/5

Hi all,

I have a 10" f/5 "Sky Mentor" (Canada) aka Orion XT10.

The secondary is 65mm (2.6") and I am wondering if I can go smaller.

I have seen 10" (Mag 1 Portaball) with a 1.83" mirror.

I know there are other ascepts of tube design that I have to consider
but is it generally possible and what I have to do in order to use a
smaller secondary, (ie change the distance between primary and
secondary ???

Any help will be appreciated.

VL