The Talmud states that a eiruv techumin may only be made for the purposes of a mitzvah. The impression is thus that once an eiruv is made with that context, it may be used for any purpose. This is indeed the ruling of the Tur (O.C. 415) and the Rama. The Sha’ar HaTziyun (#11) notes that the Shulchan Arukh does not disagree; he merely felt no need to state as much, as it can be inferred from his agreement with a bigger chiddush, that even an eiruv made for non-mitzvah purposes is valid after the fact. That last point is subject to a dispute between the Rambam, who agrees, and the B’hag, who disagrees, as noted by the Tur.

However, Rashi (s.v ein ma’arvin) apparently is of a more stringent opinion; he writes that the Rabbis did not permit one to leave the techum through an eiruv except for the purposes of a mitzvah. The implication is that even a properly motivated eiruv may not be used for a non-mitzvah purpose. R. Yitzchak Blazer (Resp. Pri Yitzchak, II, 11) adduces support for this position. (See also Sefat Emet to Eiruvin).