<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">...may make some mushy pork. </div></BLOCKQUOTE>Or, perhaps, may make some of the pork mushy.
Moisture from any source will freeze into large ice crystals if the freezing happens slowly, as it does with home freezers. The large crystals can actually cut into the meat fibers and, when thawed, make the texture mushier. Whether or not this will occur on enough meat to be noticeable is a matter of the original meat texture at the outset, the quantity of the added juice, and how fast freezing occurs. Though it will be very slow by commercial standards where frozen food is flash or blast frozen, the more time the juice has to pool in the meat at the bottom of the container the more possible that that meat tends toward mushy. It is still quite possible that no one would notice after the meat is mixed, heated and sauced but it's hard to say with certainty--how and with what it's sauced and the sensitivity of the diner(s) dining are factors as well. Might not be a big deal at all but since there is no benefit to adding the juice before freezing I agree with you, Dan, and I wouldn't either.
If there were an occasion where you wanted to freeze meat with some added flavors, say--maybe you were giving a pack of frozen pulled pork to friends and wanted it to be able to be thawed and heated and eaten unsauced if desired--but you wanted some signature flavors in there, then the thing to do to ameliorate the outcome is to mix your ingredients and emulsify them before adding them to the pork and freezing. E.g., apple juice, vinegar (if desired), rub, a little sauce, can be whisked or blended together (with a little prepared mustard and then a little oil drizzled in if the sauce isn't able to emulsify on its own, which depends on its ingredients). This process allows the mix to cling better but the oil mitigates the larger ice cryatals.
Good call on the acidity issue, Adam. As noted, it is possible that no one would notice any mushiness depending on the variables involved and were you to know it wouldn't be an issue then its possibility due to potential acidity would be the controlling focus.