Hopshot is co2 extracted hop resins. It's just like adding hops, only without the vegetal mass (so fewer losses and less of a vegetal flavor when using large quantities).
Adding it to fermented beer would be like dry hopping. It will probably not be that easy to dissolve. It is thick, sticky stuff.
Morebeer sells isomerized alpha acid extract, you can use that to add IBUs to finished beer.
I use it in IIPA, American Barleywine etc with good effect for bittering. No vegetal flavor and fewer losses to absorbtion. Never tried it as a late or dry hop. The last 4 I used, which were from two different purchases, smelled floral and piney when added to the kettle. Not sure what hop varieties are used or if the formulation changes. It is probably the same Hop Union extract Russian River and Lagunitus use though I think NB does not disclose the source. Doesn't matter though because Hop Union does not disclose what varieties go into their extract.