Welcome to the OptoForums. I believe the short answer is "yes," but let me expound on that to make sure we're understanding each other correctly.
BTW, good job thinking ahead, especially given the foreign country, 2-days thing!
Our PACs all have native Modbus/tcp support (they act as Modbus slaves, straight out of the box), so you can use a Modbus client (I use Modscan32 for testing) to read/write. Super easy.
I'd say it's a good idea to get a PAC-R (which is the not-so-dumb brain + controller) vs. just a PAC-EB (just the no-so-dumb brain w/no controller) if you have that option. Some people even buy PAC-Rs and shut of the "control engine" if that need a beefier brain.
If you want your PAC to act as a master, then that gets more complicated and would require a controller, but I don't think that's what you're asking, right?
Also check out this landing page on Modbus for more details/overview.