Let's suppose that we have a multiclassing barbarian/PRC. The character has 6 levels of Barbarian and does not intend to take any more, focusing on leveling as a rogue. However, the player would like to have an additional Rage Power. For this purpose, the player would like to take Extra Rage Power feat to select some Rage Power that he qualifies for (e.g. Lesser Beast Totem). However, the PRC he has chosen (Mammoth Rider) has no progression of rage feature.
Extra Rage Power feat says:
Extra Rage Power
You have unlocked a new ability to use while raging.
Prerequisite: Rage power class feature.
Benefit: You gain one additional rage power. You must meet all of the prerequisites for this rage power.
Special: You can gain Extra Rage Power multiple times.
after APG, emphasis mine
Can he select Extra Rage Power while taking a level in Mammoth Rider by the virtue of him being able to rage at all, or can feats that have "class feature" prereq be taken only while leveling in a class with said feature?