Euphorbia lactea cristata cultivar

Parts of it look as though the crested parts are reverting back to the regular non-crested E. lactea.

Cynthia, as Tyler above points out, it's reverting to normal growth. It can easily be grown on its own roots, but was likely grafted to accelerate its growing (which it has done splendidly). Be careful of this plant's sap - depending on your sensitivity, it can be an irritant or worse to skin, and definitely keep it away from all mucous membranes, If you're going to trim it for cuttings (or to take the load off of that graft), have some warmish water to daub the cuts in - that will slow down the milky latex bleeding.

Thanks for the info. So, if I trim it, can it be handled like other succulent cuttings- ie, let it dry out and form a scab, then put in some. Substrate (succulent mix), leave it for a bit and then water after a week or two? Also, will trimming the non-crested bits keep the reversion from continuing, or just make the plant smaller? It is kind of amazing- seems very sturdy on its graft - but that can only last so long....

Yes, but personally, I'd do what you do but only mist the cutting(s) until growth is evident; then you know it's got roots (it's not desirable to water the soil before). The plant's got both normal and cristate forms in it, so I don't think cutting one to favour the other will make a difference permanently, only temporarily.