Are you using a hosting service like nitrado or is it a dedi server?

If its a hosting service, that means you will have to restart the server while uninstall/installing mods. So what I would do, take a back up of the server, close server, uninstall the mod, start the server, close the server, install SMM, start the server, make sure SMM installed properly, close the server, start server using the previous backup. Make sure no players logs on the server while the process is ongoing.

If its a dedi server, you maynot have to restart the server while the process but in any case, steps above would be the safest.

We have a dedicated server with a cluster of maps (Island, Center, Scorched Earth). To clarify since you haven't stated it specifically, if we follow the process you described do you expect that our mats will transition across? For example, if we had a large storage box full (45 stacks) of metal (5000 each) with stacks plus mod running, after following the process would we still have the same mats stored?

This is what I expect to happen. Lets say I delete SMM from my server and go back to orginal ARK stacking values. Any item I had stacked before will be set to ARK default stacking values.

Or viceversa, if I install SMM on my server while I had ARK default stack values, any item I had will remain same and only new gathered/obtained items will stack with SMM values.

So what matters here is the base item weight values. If its the same on both mods, you wont lose any, if not, base weight values will convert into the higher one.

I would also like to mention that this is what used to happen but I am not playing the game myself for quite a while. So Im not sure if the behaviour is the still same or not. To make sure you can try on a local server on ur own pc.

It took us a while to get around to it, but it appears we've successfully managed to transition from Stacks Plus to Stack Me More by following your instructions above. Thanks for the help!