So I think I will
For the purpose of [epic] feats, prestige classes, and other options, a character is considered epic at 10th level instead of 20th level. After 10th level, regular feat slots may be used to acquire [epic] feats. All other prerequisites still apply.
A substantial majority of [epic] options still require 20+levels worth of ranks in skills, however. Rather than institute an across-the-board subtraction of 10 from all [epic] skill prerequisites (leaving many requiring fewer ranks than pre-[epic] things), or from all skill prerequisites (leaving many pre-[epic] things with no skill prerequisites at all), I will go with my old "add a new option and make it a feat" standby:
Prerequisite: Skill Focus in the skill selected
Benefit: For the purpose of of qualifying for feats, prestige classes, and other options, you are treated as though you have 15 more ranks in the selected skill than you actually have.
Additionally: Epic Spellcasting is completely broken. But I'm going to allow it just as it already is, except that actual epic spells don't exist. You can use epic spell slots only for metamagic'd versions of regular slots.