Yes they should work no problem.

But there's always a possibility of issues.
One revision may work in your version 2 but you should also look for upgrades for all your 3rd party plugins to ensure they carry over to the new version.

For example your paths to your plugins may get shifted.
I take a screenshot of my "Options" window showing those paths before I do upgrades just to be sure I know what they all are. I may take screenshots of my Audio setup too.

I believe the sound engine in Studio One changed somewhere between version 2 and 3... whereas the PreSonus native plugins like their Compressor, Multi-band compression, etc. will have changed... thus potentially changing your sound (louder or quieter) on tracks containing those.

Important: You can open a song made in ver 2.xxx with the latest version of S1, BUT:
If you simply save the song in ver 4.6, you won't be able to open it in the older version of S1.
You will want to rename the song when saving in 4.6, so a different file is created, just in
case you want the original song to be available in S1 ver 2.

I just read that Version 3 is no longer available to download which sucks. I not going to pay another $149 to get version 4. I am I wrong?

I logged onto my account and found out I could download version 3 which I am doing now. However, it is really slow on Transfers of the Presence XT Core components. I am hardwired to my router. I can't believe how long this is taking. Is this normal? I am only on the first one which is Acoustic Guitars and there are about 10 or more left. Look like I'll be here all day. I don't remember Studio One Version 2 taking this long but maybe it did.

Okay my last time complaining. Going on over 3 hours now and it's still load Presence XT Core Acoustic Guitars. I have really high speed internet. PreSonus, this is insane. Probably the last time I update something.

It doesn't all have to be done at once. I installed the program and was using it for some time before I setup the sound sets.

I might have to do that. I took close to 8 hours for the Acoustic Guitar sound set to try and load and at the end it said failed. So I stopped all the rest and restarting the program. I restarted the program, The Acoustic set has been going since about 11:30 PM last night and now it's 8:00AM . That's 9 hours and it's only at 600MB out of 1,90 GB. This is insane. I might just stick with my Version 2.5 Studio One Pro and call it a day.
This is crazy, I was going to try and update to version 4 but I am not paying $149 to wait days for my sound sets to load. I love the program but this downloading is insane.

I didn't change my sound sets between 3 and 4. I think they stayed the same.

On the bright side, you can use ver2 just like before. But if you like some features of
version 3, just go as far as you can with ver2, and then continue in version 3 (but again,
use "SAVE AS (new filename)" if you want to be able to open the original in version 2.

Also, once or twice, I had some slow transfer times. I aborted after 5 minutes, and restarted.
The transfer then went WAY faster. I have no idea why, but sometimes that happens.
Maybe you could start a transfer when your done with whatever you're doing in S1 for the day.
If you're not going to use S1 overnight, maybe the inconvenience isn't so bad.
** As Tacman said, the instruments that you already have (probably) don't need to
be reloaded (sorry, I'm not 100% sure, but I'm pretty sure)

Thanks for all of your comments and help. I put a ticket into Support just to see what they would say. I was told because everyone is home, even Google is running slowly.That was their response. It took all day but I did get the sound sets installed and their is a difference between 2 and 3 with Presence XT. One of the main reasons I wanted ver 3 is iPad remote.My faderport USB wire isn't long enough for my situation so the iPad is helpful. It will be a cold day in hell when I pay $149 to upgrade to 4. For what I use it for, 2.62 was very stable for me. Let's hope I can say the same for 3.

So did you solve your issue?