Caliper piston question

[Yawesh]

So let's say the piston is sticking out, would C-clamping it back in with the brake reservoir cap off and many towels wrapped around the reservoir capless area it be ok?

Or it is required to remove the bleeder plug and hose?(thus, requiring the tedious task of bleeding brakes....).

Just worried that the bleeder plug acts as a primary 'gate' that if not released first while C-clamping would cause it to 'blow'

Thanks everyone!