Re: Mixed Media over oil paint?
I don't think this will work any better than mixing oil with water. It's essentially the same thing.
Also, oil oxidizes and hardens, it doesn't dry, and it can feel 'dry' to the touch but is still not hard throughout. Depending on how thick the application is and what pigments you used, it may not be entirely cured yet.
'Fat over lean' is the rule. Perhaps there is a medium or sealer that will allow the type of application you're wanting to do, but I don't know what it would be.
You might call Gamblin. They are to oils and alkyds what Golden is to acrylic, and they might know of or have something. There are impasto pastes that can be used with oils (like thick gel mediums for acrylics can be mixed with acrylic paint) but I don't know if they can be used alone for a modeling paste effect, or if they could be applied over oil paint.
I think Windsor Newton makes a gel paste for oils, but I don't know if it would do what you're trying to do.
But I don't think an acrylic paste over oils will work over time and there will at some point be a failure between your layers.