Did the melding between the two change after Rand had his hallelujah moment on the Dragonmount? Could Rands current state of mind induce a change in Moridins?

Moridin already seems to feel the pain of Rand's missing hand (TGS Prologue). Earlier, Rand seemed to have been picking up Moridin's nihilistic attitude (can't find the reference, sorry). So there's already a mental interaction of some kind. And judging by the effect Rand had on Torkumen at Maradon, I would confidently expect the effect on Morididn to be as devastating.

Did the melding between the two change after Rand had his hallelujah moment on the Dragonmount? Could Rands current state of mind induce a change in Moridins?

Probably, but probably not enough. The dream in the epilogue is a clue that Moridin is still evil.