I'm concerned about it. Last week the barrel touched his arm and left a huge burn on his arm. The barrel is getting very hot.
If you shoot it enaugh times in a row it will get hot no matter what choke it has in it.
Because of the burned powder in the barrel.
Rifled slugs are made of soft lead so I don't think it will hurt the gun.
But if you are worried you can check with a gunsmith.
Modified choke is not much tighter than a impoved clynder.
You could try an improved cylnder it might improve the pattern.
This is JMHO so check with a gunsmith.
But I think it should be OK