I doubt your extractor is going to be the issue here... and taking advice on this conversion from non-gunsmiths is worth about what you are paying for it.....
Opening a bolt from standard to magnum requires removing a bit of material off the bolt face rim so the larger diameter cartridge will fit the bolt tightly. Going the other way, however, is going to involve replacing the bolt, or, if it was a two piece bolt, replacing the front sleeve with bolt face. You need to talk to a gunsmith to see the best way to go with this IMO.
Keep in mind if this Model 7 is a magnum and you are going to a standard caliber you may need to also replace the box and follower for it to feed properly....
Seems like it would be cheaper to replace the bolt with a PTG bolt made oversized and have it fitted to your blueprinted action ... but I'm not a gunsmith so everything I said could just be nonsense....
Bob