Assistance with Feat: Legendary Size from In the Company of Dragons Expanded

[tekknowkub]

I am trying to program the following feat from the Pathfinder sourcebook In the Company of Dragons Expanded. I have the base In the Company of Dragons source already purchased and need some assistance on how I can add this as a feat. The material also says there is an adjustment in HL for Dracomorphosis but I can only assume it was removed at some point because I can't find it.

Legendary Size (Dragon)
You are a dragon of truly prodigious size.
Prerequisite: dracomorphosis class feature, character level 8th
Benefit: Increase your effective level by 2 when determining the effects of dracomorphosis. If you have at least 20 class levels in classes with the draconic hero archetype, gain the Colossal size and other benefits of the draconic exemplar’s great wyrm class feature. If you have at least 20 draconic exemplar class levels, gain an additional +2 size bonus to Strength and Constitution.

How do I grant the Great Wyrm [cRPDraGrea] class special ability at level 20?

I'm using the following but its throwing an error.

if (HeroLev >= 20) then
perform hero.assign[cRPDraGrea]
endif