So from what I understand you have a section which needs undo/redo features and once complete goes into the store right? Typically I would say this sounds like component local state. If you want though you can of course use another instance of the store (new Store(…)) for this sake.
To give you a sample where I used a second store instance is the log panel of the IDE I’ve worked on. While the whole IDE is part of a default single store, the log panel created a second instance due to high throughput and history support. The only difference here is that this was purely ephemeral state which didn’t come back into the global one. So you would have to make sure to store it with a global stores action and on a new start rehydrate the initial state of the substore to the previously stored value.