Welcome to the forums! The ZP3 is a great phono.

There are two modifications that you can have done at the factory. First, beeswax caps, this is higher quality capacitors. Second, the 25th anniversary mod is a maxed out power supply.

I have not heard the difference between modded and nonmodded. Everything I've read is the mods take a great amp to the next level.  bottom line if you can, just get the mods and enjoy.

If it's a possibility now, get the mods. If not you will need to send the amp back to the mothership and get upgraded at a later date.

This is a very long tread about the development of the UFO25th, after Steve finished that work of art, transferred the knowledge to his other designs and named them the 25th Anniversary Mods.

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1510887200

ANS - Welcome aboard! As explained, mods (modifications) are upgrades Steve has come up with after the original prototyping the units, finally deciding on the product and making it for sale...then years later when he learns something else while working on something else, he incorporates it into one of the other AMAZING products Decware makes. IF you have the cashish to part with now, get all the mods/25th anniv. things you can afford. When I bought my Decware gear, Steve didn't have the 25th anniv gear thought of much less designed. I KNOW it's better than my Decware gear with various upgraded caps etc, etc. Get what you can afford. You will not be disappointed. After over 45 years in the hobby, business I have NEVER looked back at my Decware purchases with ANY regret....hell I am on the waiting list for another piece. Ask questions on the forum and Happy Listening. Chris.
P.S. The ZP3 is the best phono stage I have had, ever. Killed my Audio Research SP-11, Modifed NYAL, Krell, VTL...you get the pic.