Can I be meyached (make not muktza) something that doesn't belong to me? Is there a difference between something that is hefker (ownerless) and owned by someone else? It seems from the gemara in Shabbos about the talmidim of Rebbe, who were meyached things to sit on before Shabbos, that one can be meyached things that are hefker. Is this true?
In regards to being meyached something that belongs to someone else, is there a difference between being meyached for one shabbos and being meyached forever? It's kind of hard to hear that it is possible to be meyached it permanently if it isn't mine, as the owner can just decide that he wants to do something else with it, and I have no say in the matter. Does zochin li'adam shelo bifanov tie in at all over here?
Does anyone know of any sources for this?