Mutton tallow generally doesn't spoil easily if at all, not like some other tallows and greases. If it did spoil a bit, no big deal, yer patches and balls won't mind it a bit.
I have 3lbs of mutton tallow left that I got from Dixie Gun Works about 6 years ago, packaged in translucent plastic LDPE containers and the tallow looks to be okay. I use it to make GatoFeo #1 lube for ball patches, melted along with pure beeswax and canning wax, then rubbed into strips of cotton patching cloth and either melted in with a heat gun or left out in the sun. The result is a bit harder lube that doesn't rub off onto everything like pure tallow does, and I roll up the patch strips and pin a strip onto the strap of my shooting bag for easier use during gun loading. I keep the tubs of mutton tallow in the dark, stored in a cool basement.