I use a Poly Wad Yellow solid disk spreader insert. Same powder charge and shot weight (3/4 oz) as my regular 20 G loads. Only difference a 7/8 oz wad which leaves a little room for the spreader disk. At the wad insert station I put the plastic regular wad in, throw the shot then use the PW 375 wad seater to insert the spreader disk. Only extra step is the 2nd wad on top insert It patterns very well at quail distances in my 28 inch F&M Parker Trojan. I just used that gun and load to qualify for a Parker "Doubles" pin on Quail. First shot was close, to make some time for a good 2nd. Quail was fine not torn up at all.
On altering, as has been said it's going to hurt value. I guess there are good choke opening gunsmith out there. However looking at Parker's with open chokes for several years now most are "messed up" to my standard this after checking with a dial indicator choke gauge. Number of guns ruined by poor choke work has hurt the value of any gun who's chokes have been altered.
Look at this video from Midway how to ruin a Parker in a few easy steps, by buying the tool from Midway.
https://www.youtube.com/watch?v=l6yrnJIyjtU
William