I'm wondering whether the Ring had a role in these physical changes.

I'm not sure about the slime, btw : whether Gollum exudes it, or merely likes getting messy. In LOTR we also encounter him as 'snuffling' (tracking by smell) and as having a most un-hobbit-like ability to climb head-first down a cliff. For example he has 'pale lamp-like eyes' (for dark vision?), and long, bony fingers.

I notice that Gollum has a number of what look like adaptations for his lifestyle in the dark among rocks and pools. What happened? And did the Ring have anything to do with it? So, although it's not completely explicit in the book, I'm thinking that the Peter Jackson movies got it pretty much right: showing Smeagol as a hobbit initially, and Gollum as a something much monstrous (rather than Smeagol looking like he does later, but jolly and better dressed) He was looking out of his pale lamp-like eyes for blind fish, which he grabbed with his long fingers as quick as thinking.' He paddled it with large feet dangling over the side, but never a ripple did he make. He had a little boat, and he rowed about quite quietly on the lake for lake it was, wide and deep and deadly cold. He was Gollum-as dark as darkness, except for two big round pale eyes in his thin face. I don’t know where he came from, nor who or what he was.

'Deep down here by the dark water lived old Gollum, a small slimy creature.

Lord of the rings frodo becomes gollum