Thanks for your reply. Skimmed milk contains almost no fat so it cannot really be homogenized. If I add unhomogenized cream to skimmed milk, the fat globules will be bigger (~3.5µm) and more intact, resembling the state of the unhomogenized fat globules. I have asked the cream company if they homogenize their cream. There would be no point to add this cream to skimmed milk if it was homogenized to go back to the equivalent to homogenized milk. As for UHT pasteurisation of cream, not really a problem either since the vast majority of proteins would come from the HTST pasteurized skimmed milk so the curd should form as for HTST pasteurized milk, with some help from CaCl2.
If anybody has tried the cream + skimmed milk combination, I would be very interested to read your experience with that.
Otherwise, I will make the test with small cheeses when I have the time and come back to let you know if it worth it.
Addition - From Dairy processing handbook:
Products of high fat content are more difficult to homogenize and also more likely to show evidence of fat clumping, because the concentration of serum proteins is low in relation to the fat content. Usually, cream with higher fat content than 20 % cannot be homogenized at high pressure, because clusters are formed as a result of lack of membrane material (casein).