Thinking about the next update to UF and Spirit

When the next update comes out (I am running Spirit/0.1.6 and UF/0.2.7.1). will it kill all the customization I have doe to the css code.

How will it affect the custom pages I have built and the formatting changes I have made?

I just installed Snapshot and will begin daily backups as soon as I figure it out. Will that be adequate in case a new update ruins customization?

Thanks.