So I was pondering the options to make mythic chars have the opportunity to take side trips/etc into non-mythic adventures at the 'expense' of suppressing some of their mythic might.
I was thinking of making it a mythic trait available to any mythic of (possibly) tier 5 or less with the following effect:
(The name is still a work in progress)
Effect: You can suppress the draw of mythic fate by temporarily suppressing your mythic might. A mythic character of (tier 5?) or less can suppress their might down to Tier 1, temporarily losing access to all gained mythic feats/abilities/etc of their higher tiers, but will now face non-mythic, or low-mythic encounters instead of those matched to their true tier.
These reduced mythic encounters do not count as trials and while suppressed a mythic cannot gain a new tier.
Mythics of tier (whatever) or greater cannot benefit from this trait, as they are too heavily involved in mythic fate to be able to easily step away from it.
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So basically the idea is that you sorta can run with things closer to your level-based CR and not have to worry as much that 'oh shit, look, another f%!#ing demon lord!'. At the same time you don't get to keep using all your mythic abilities to make those reduced (non-mythic) CR challenges super easy.
By rationale I'm also saying that beyond a point (when your passives get a bit too much, like tier 5 and more) you get more into reality warping that can do stuff like save your ass from getting killed/etc. And would likely come into play whether you wanted to suppress it or not, if some non-mythic threat managed to do significant harm to you.
So its an IC and OOC effort, signalling when the party wants to not have to run mythic stuff for awhile, but also trades in some of their power for the duration.
Suggestion: Tie mythic powers to items or other external sources. Then heroes can be situationally non-mythic by leaving their magic rings or super suits at home.