Will fish that are stunted grow to a large size once the issues causing the stunting are resolved? Are they forever stunted and its their offspring that will grow large?

I have personally observed 8-10 inch LMB grow to 14" over winter when transplanted to a new pond with a stunted GSF population in the fall. They'll eat if they can and how fast they grow depends on how much they consume. They may have been 7 year old 8"-10" fish when they were transplanted. So obviously they might only have had 3 or 4 years left to grow. I can tell you they were obviously stunted when they went in with heads too large for their bodies. Following spring, their bodies were fat and the heads were well proportioned to the bodies.

In a setting with an existing population the resolution of conditions that lead to stunting is not easily resolved to allow LMB to grow large. But the size and condition of LMB can be greatly improved by harvesting LMB to reduce competition. Again, just like with the example above, they have to consume forage to grow and if there is sufficient forage they will grow according to that consumption.

Every day without enough calories is a day of growth lost. Can they grow large? Maybe but don't worry about it affecting their genetics if it's only a generation or so.

You bring up an interesting point: While the genes wouldn't change, perhaps the expression of those genes would, usually described as epigenetics. Fish stunting due to inadequate food might lead to adaptations in progeny designed to minimize growth so as to maximize scarce calories for survival. Not saying that's the case, but it might be. Would be an interesting research project.

PB mag has several articles on adaptation vs evolution i.e. epigenetics vs genetics.