I’ve always broken them in two and never had an issue. And really, it’s the only way to clean out the dust boot and fluid seal grooves completely. Here’s what I’ve done in the past.

1 Break the caliper into two pieces, you can do both at once if you want, it’s impossible to mix up the pieces.
2 Remove the piston, seal and dust boot. Since you’ve already done this should slide right out. In some cases it requires
heat and other persuation.
3 Clean out the dust boot and piston seal grooves. I use a Dremel tool with a small cutoff wheel for the dust boot groove
and a stone for the piston seal. It’s nearly impossible to damage the caliper body with these. The cutoff wheel will
remove all the caked in dirt and rust and it’s easy to tell when they’re gone and you’re starting to remove metal as the
feel will change. With the stone you can remove and bumps and rust that may have gotten into the piston seal groove.
You can also use it to clean up the area from the top of the seal groove to the top of the piston opening since that’s
where it tends to rust and get dirty. This should allow the piston to move freely.
4 Optionally you can now clean the two halves and paint them to prevent future rust gathering on them. Don’t paint the
surfaces where the two halves come together, the piston wells or the mounting ears where they mount to the stub axles,
althoug I have lightly primed with epoxy the surfaces above the piston seal to prevent further rust formation.
5 Once whatever cleaning you want to do is complete you can reassemble. Insert the piston seal and dust seal into their
grooves, should slide in easily since they’ve been cleaned out. Insert the piston. The piston should slide in with no more
than the pressure of a couple fingers, if it requires much more than it may be cocked or the piston seal might be out of
place or undersize. Push pistons all the way to the bottom, I find it easier to bleed that way as there is less trapped air.
6 Reassemble the two halves and don’t forget the square section seal between them. I’ll wire wheel off the bolts to have
clean threads so I get accurate readings while torquing. I’ve used 45lbs for the small bolts and 50lbs for the larger ones.
Never had a leak or problems so far and the first set I did have been on almost 20 years. Torque about 1/3 each time, I’ve
gone smal to small, large to large. But like I said, never ran across anything factory with details.
7 Reinstall.

One other thing to note, sometimes you find small shims between the caliper and the stub, these are for centering the caliper in relation to the disc. Make sure you reinstall them if present. And if you haven’t yet, invest in a new set of flex hoses since they eventually will start to fail internally.

Any questions, please let me know.