Can epoxy resin be reused?
Yes and no.

In general, yes, epoxy resin can be re-used. It's supplied in two containers, you measure and mix only what you need, taking great care to avoid cross-contamination when handling the two parts. West Systems and other marine epoxy products are designed for this.

That pack however is intended for easy mixing. If used as intended, that prevents reuse, as you mix it in the pack before opening.

You might be able to decant each part into separate containers, then measure and mix as normal, keeping the rest for future use, but it'll be a messier process than starting from separate containers, and you'd better not expect any guarantees from the supplier if you try.