Dear Isteak

The 95U and 100 U are considered from the same family i.e they share same back plane bus and modules. However the concern is that the 95U is a little bit more sophisticated than a 100U i.e it have built port ( High speed counters and onboard analogs) also depending on the CPU 95U you had you might have an additional port also either for serial or profibus communication. Also the standard block library and DB1 would be different. Do not also forget that the 95U does have onboard inputs and outputs which would have to be added as extra modules in the 100 U if they have been used on the 95U.
I am putting a reference to the 2 manuals below for your reference
95U
p://support.automation.siemens.com/WW/view/en/1091648

100U

http://support.automation.siemens.com/WW/view/en/1091978

Regards