Yes it's easy enough, though not a fast job to tackle. I bought a spare fork (top pic below, regular fork bottom pic) for my Thorn audax and left the steerer long in case I want a higher riding position in future. You will need to have a crown race (for example
Link: FSA Crown Race XLII) compatible with your current headset put on the new fork, and a star nut fitted and get enough spacers for the amount of steerer tube. If your second fork is set higher than the original you may need to fit longer cables to reach the bars, you only need to do this once.
To change forks just undo the top cap on stem, side bolts on stem. Unbolt front brake callipers, pull cable outers from cable stops on frame, slide out fork. Take care not to kink/damage cables whilst handlebar removed, I secure the bars to the toptube with toestraps while swapping the forks.
Clean and smear some fresh grease on the headset cartridges whilst they are out, observe how everything fits together on the headset. Slide in new fork and bolt everything back together (watch YouTube vids on how to adjust headset/brakes if required). If you run mudguards it would be worth fitting the spare fork with its own guards.
I have two sets of wheels for my Thorn audax, Chrina rims with 24mm tyres for summer/audax rides and Sputniks with 28mm tyres for touring/winter riding. When swapping the brake cables need to be tightened/loosened for the different rim width, check the brake pads for alignment on rims and adjust if required. Both wheels have the same LX hubs so the rear gears don't need readjusting, and their own cassettes and chains. I just put the wheel in swap chains (they have quicklinks).
