If u said whether it's the inline modern type or not I missed it. If it is u'd be ok to take the breechplug out and pour the powder out the back unless it is pellets. If it's pellets U can take the ramrod and run it in from the breach toward the muzzle. If it is not inline, it's a whole different ball game. I saw a CO2 cylinder that had a adapter to screw into the hole where ur nipple is screwed in. I've nevr used this as I always just shot out any load I did not want in the gun for whatever reason.
I have 2 inlines (I bought one for my dad). I never shoot them unless I'm at the range or shooting at a deer. At the end of PW season, I push the bullet and pellets out the breech with the ramrod and put them back in the corner of the pellet box. Those 2 loads become my first two sight-in loads the next season. I then clean both guns thoroughly and reinstall the breech plug with anti-seize lubricant before storing them for the next 11 months.