The quoted example is gramatically correct, but poorly written.
The reason for this, and your confusion, is the word "impacts": it can be read as both a noun (the effects of the thing) and a verb (creates an effect). The sentence, as written, forces your reader back-track and re-parse your sentence to see if "impacts" is a functioning as a verb or noun (apostrophes are easily missed, and often misused).
To prevent your meaning being carried by a tiny punctuation mark, I would suggest this re-wording:
- This rebalancing of the impacts of customer classes on on the system means there will be uneven impacts on rates the first year.
Note also that one cannot have an impact to something, only on or upon that thing. It's also pretty poor writing to use "impacts" twice in once sentence - "effects" is probably the noun you're looking for for in one of the two cases.