Does moist heat and lid message for blepharitis cause corneal damage?

Would not cause any ocular damage if temperature is mild or lukewarm, and massage is gentle.

If the heat is not over 110 degrees and the pressure on the lids is gentle the cornea is not going to be damaged. Thermal corneal burns heal well when they do occur (e.g. curling iron). Try to pinch the lids so they squeeze against each other, not against the eyeball, which can raise the intraocular pressure and potentially cause other damage especially if you have had eye surgery.