What sort of changes are you thinking of making? I ask more out of curiosity than anything else, since I doubt there are many non-content changes you could do that are likely to harm rankings (unless you change URLs or break something).
To my knowledge Google does not really have a model of pages that "should be static". Similar sites I've had that have not changed fundamentally for several years, but have gone through various iterations of changed links/templates/css etc. have never experienced any problems. There's certainly no "penalty" for doing so, anyway.