As far as I know, it isn't very plausible or easy to change the version of JRC at the moment. The good news is each version has potential still and has somewhat unique strats each but it is annoying to not be able to switch versions as we like.

Version 1.0 is the first version of the game launching on June 15th, 2020. It is currently known as the slowest version of the game and for most is extremely hard to access. For those who still have this version of the game, I think it would be awesome to see one or two more WRs before giving up on it but generally, this is denoted as a legacy category for the reason of no runs in around 6 months (for a fair reason) as of this posting.

Version 1.1 from July 1st, 2020 is the currently known fastest version of the game and it's looking to stay this way until we are able to get around something in 1.2 more efficiently which I'll mention in the 1.2 section. This version is seemingly up to twice as fast as 1.0 mainly due to a trick we call DUMs (double-under manipulation) or DJMs (double jump manipulation). 1.1 added the double-under/double jump ability which seemingly doesn't do much other than introduce new cool-looking high-speed animation, but with this we can cancel the animation of a regular jump, counting it as two jumps per visible jump (doubling speed in the process). When you shake at a specific rhythm DUMs become insanely consistent. 1.1 also added new costumes/backgrounds and added some polishing/new text. If you have this version and want to stay on the fastest version, I recommend keeping it for now.

Version 1.2 from September 8th, 2020 was an attempt to erase or nerf the DUMs technique/exploit. In reality, it's simply more difficult to pull off a DUM and as of the early runs of the game, I can only find certain instances of DUMs occurring. One way to get DUMs to activate is the same as before, a normal jump to cancelling it with a double jump, but it is much slower to repeat this than before as it seems to lock into doubles jumps more easily, making it harder to cancel repeatedly. 1.2 also supposedly polished the game further and added a 100-day summary mechanic. This version of the game has the most chances for improvement and findings in my opinion and I won't be surprised if it comes to being over 10 seconds faster than 1.0 one day (in 100 Jumps), or maybe even getting close to 1.1 pace.

As far as I know, Switch games on the eShop automatically load the latest version of the game so if you do jump into the game now or update on accident, you will be stuck on 1.2. Pretty ridiculous that until we have access to things like version swapping, the only way to access all 3 versions is 3 Switches (and a time machine if you miss a version)... If you are on your preferred version, please be careful about the auto-update setting, or accidentally accepting the update when it asks you (Internet off/airplane mode might solve this too).

TLDR;

• 1.1 is the fastest currently
• 1.2 is still fast and has the biggest potential but with new similar strats required
• 1.0 is the slowest but purest
• It is currently not possible or easy to change versions (turn off auto-update/turn on airplane mode if version updating is a concern)

Happy jumping!