I wholeheartedly agree with creating another rank for these folks. I've been in this situation, and ruffled feather simply does not describe the situation when you boot out long-time, founding officers to make room for new blood who will help with the day-to-day duties of a raiding guild.

First Blood more accurately describes it. XD

Anyway, the other advice in the comments is also potent- the third 'leadership' type rank should have a few characteristics:
1. Name it something innocuous but flattering- Elder, Council, Advisor, etc.
2. It should almost certainly be obtainable for new(er) members. ('Founder' rank flounders a little more often than we'd all like.) You want a clear policy on what it takes to gain the rank- for example, being a retired officer, having contributed to the running of the guild, but being unwilling or unable to fulfill an Officer's duties, either ever, or at this time, etc.
3. Elaborating on above- it, that is, the policy on this rank, must be PUBLIC. If people know, oh, that's the rank for officers who can't be officers right now, for whatever reason, that will minimize hurt feelings (note: minimize, not eliminate. Eliminating hurt feelings when running a guild is like creating a perpetual motion machine- it is not physically possible in this universe- ahm- or Warcraft's.) You will eventually forget to emphasize this, and someone will mention- Hey, why are all these guys at rank 3, where I'm only rank 4?! (They'll use Wow-heroes or the like to check, even if you name the ranks the SAME.)
4. The rank shouldn't get TOO bloated. If somebody really takes a 3-4 month hiatus, somewhere around the fourth month, make them MIA, or whatever your equivalent is. (We actually have an MIA rank). Restore their rank when they return, or, if you have the inkling that they won't mind, just give them regular guildie status. Being sure they understand that they'll go to MIA status before they go on hiatus will help if they're particularly sensitive.

I'm sure there are a couple of other must-have attributes for the rank, but this is the best answer I've found, so far, to sedating buddies gone wild for power and respect, and making sure that new blood doesn't feel like they're second class citizens.

In essence, you're just making an officer, second class.

Retired officer works too, for simplicity's sake. (You know, in a way, I wish almost everyone WOULD reach that rank- they'd all have a taste of running a guild, and I think average patience levels would rise astronomically!)

I love the advice about extending the duties to others, and wholly support it. Delegating responsibility while still showing that you're working hard is perhaps the most important thing you can do as a GM. Delegate everything, and don't show signs of thought and work (or being so insular that no one ever KNOWS how much thought you put into how to get that 25-man up and running, or just what/who that other 10-man team needs to get rolling properly) is a great way to burn your OFFICERS out. It's all a balancing act, and in a powerful way, it's part of the game- the most dangerous, real, frightening part.

Good Luck, OP, keep on truckin' and having fun! :)