HLM-Longitudinal Analysis: Moderation in level 2 variables?

I am creating a growth model using HLM 7 where Level 1 is Occasion and Level 2 is Person. I am trying to see if I can test the moderation effect of one level 2 variable on another level 2 variable (does propensity for excitation (L2) moderate the effect of mood (L2) on arousal over time(L1) ?) but all I am finding on moderation in HLM is related to cross-level moderation not within level moderation. If anyone could provide some information on 1) if this is possible, 2) how to test within level moderation, and/or 3) possible sources to learn more, I would be incredibly grateful.