Yes, you can now replace your factory barrel with a threaded barrel in Production (App. D4, 21.3) and Carry Optics (App. D7, 21.3). Just remember that Production guns still need to fit in the USPSA box.
Yes, these types of holsters are legal, but be aware that the retention hood needs to be used. Many new competitors think that the hood does not need to be engaged after the loaded gun is holstered and prior to the start signal, but it does. Hoods are considered to be the same as retaining straps and must be engaged before the “Standby” command (188.8.131.52).
No, holsters with thigh straps are considered to be tie-down rigs and are prohibited per the rules (184.108.40.206, and see definition of ‘tie-down rig’ in App. A3). If you can detach the strap from the holster, you can still use that holster minus the strap. Just make sure that the heel of the butt of the handgun is even with or above the top of the belt (see this post for more info).
Per the 2020 rules, conversion barrels are now legal in Production and Carry Optics. The restriction that the barrel must be the same caliber as the factory barrel was removed (see App. D4, 21.3 and D7, 21.3).
Yes, some of the guns that are approved for use in Production and Carry Optics do come from the factory with a removable mag well. But, if you would like to shoot these guns in Prod or CO, you will need to remove the magwell since magwells are specifically prohibited per the rules (see App. D4, 22.4 and D7, 22.3).
Only pistols on the approved Production Gun List are legal for use in the Production and Carry Optics Divisions. We get many requests from members to add a pistol to the list, but requests must come from the manufacturer (here is the form for the manufacturer to submit). There are minimum requirements that must be met for the pistol to be added to the list.
No, because of special condition number one in appendices D4 and D7. Single action only pistols are not allowed in Production and Carry Optics.