Ok , so with the weapon upgrade that comes with pathfinders you can fire the single white at range 1-4 or reconfigure to fire the red at 1-2. Or vice versa...got it...

However, you CAN choose to fire the base 2 dice weapon at range 1-3 at any time right? No reconfig necessary....am I correct?

I may or may not fully understand your question based on wording yet will do my best to answer from what I know.

If using the Pathfinder unit with the armament upgrade A-300 Short/Long Range Config, at step up you choose which side will be face up. Which you will be stuck with until you recover that unit, giving you the option to flip the card over. You can only use one side or the other, which is the side facing up.

The A-300 Short/Long Range Config upgrade is it's own weapon, totally different from the Pathfinder unit default weapon A-300 Blaster Rifle. Upon attack given able to attack based on the rules about that, you may use the default weapon only, default weapon with the upgrade weapon, or just the upgrade weapon. All the Pathfinder miniatures have both weapons able to use, but only one among the two per miniature can be used though.

Only the upgrade card A-300 Short/Long Range Config has Reconfigure keyword, the totally different and default weapon A-300 Blaster Rifle doesn't have reconfigure keyword so it doesn't need and cannot reconfigure.

If that's what you were saying, yes you are correct.

The Armament upgrades are weapon upgrades like Grenade and Hardpoint upgrades. FFG forgot to include them in the RRG update, but simply apply the same rules to units with an Armament upgrade as you would a unit with Grenades, option to fire either weapon.