Discussion of table top roleplaying games.
I suppose the solution IS to spend one session on it. You need to check if everybody is alright with all rhe changes and the best way to do it is in a session 0.
I suggest sending them the pdf early and then discussing together.
Also, from my personal experience, it's better to introduce homebrew rules slowly. People get overwhelmed by a lot of stuff all together. You can discuss the overall plan at the beginning and then itroduce the rules one by one session after session.
My 2 cents: Rule changes should be shared immediately and agreed upon by the party. The GM is not the rulebook; the GM is the arbitrator for situations the rulebook does not cover. The rules should all be ones the entire group likes, or at least can live with.
Extra content (feats, spells, etc): stick it in the world somewhere and let your players find it. Nothing's cooler than beating a miniboss and finding an entirely unique spell nobody else has.
I like this idea, but given that players never read the rules, it's a little like asking my granny what kind of package management system her computer should use.
How complex are your rules? If it's more than a page or two, it's probably too much. There's a reason nobody knows Pathfinder's grapple rules. Cut it down to level you could feasibly expect someone to read in a few minutes.
My game has fewer rules than Pathfinder by any measure, although 'a page or two' seems a very low number - that sounds more like a little zine than a fully-fledged RPG.
As a general rule, at least in my experience, players don't read. Unless they request a pdf, I wouldn't bother.
Personally, I would bring it up in Session 0 without getting too specific, just the big changes you plan to impose. Then warning players if they make character build choices that would be impacted that you're not going to use RAW.
house rules : tell them right away about those. Ask the to repeat the rules and ask questions. its very important that you make sure theu know them
feats & spells: give them a doc with them. Spells and feats re complex enought they will need to reread them.
One of the things that I haven't seen mentioned yet is that for mechanic changes you can drip feed the new rule sets one per session with tailored encounters to make sure they come up that session. After the players have experienced it you can talk together to see if it is working the way you want and if you should keep, tweak, or cut the homebrew rules. Then for the next session you can introduce another new set of rules. That way people can ask their questions about the rules and only have to learn one new set of rules before each session.
For anything that fits in a list or is only relevant to some classes/roles such as expanded feat or spell lists letting the players see it in advance so they can build around it would be appreciated in my groups.