So far as modifications go, that's simple enough, make them out silicon or similar and simply glue them to the skin (I'm not sure silicon itself would adhere to the rubber). Just make sure whatever you are attaching is not heavy and is not in a high stress area where the skin needs to be able to stretch. On the head wouldn't cause issues, nor would the back for most part, on the neck and tail you'd want to place them on the 'scales' where there is less stretching.
Working wings would be difficult, any holes or slits in the rubber is going to create a weak point which may lead to further damage. You absolutely cannot utilize the cables as they run right through and back and cannot take additional strain, they'd also be running the wrong way to utilize in a flapping motion without some gears which would require a housing (there's no room at all in the body cavity). Having said that, static wings such as mine could be affixed across the back, and you could possibly make them foldable, using a similar method to above. If you really wanted flapping wings you would have to have an external gear box and motor.