You should make a term which they all fall under, just create a new field and use something like =left(Site Name , len(Site Name) - 8) which will make a new field that only says "www.mywebsite.com/fundfactsheets?ISIN=". You can then aggregate against this new field for page count. Note doing so will only give you a single column where all entries says 14.
In addition to many other (simpler) text processing options like the option above, Omniscope DOES support RegEx parsing, manipulation and re-writing of strings, e.g. you can use the REPLACEREGEX function to add new, manipulated text columns to your data set that aggregate, visualise, sort, filter and search better than your source data strings, such that your audience has a better interactive experience.
If simpler text processing options do not do the job, let us know the requirement together with a sample of your data set and we can help with the RegEx formula field.
You can also set text filter devices to implement/parse using RegEx by setting the filter type to 'Text Search', and under Search Type selecting the 'Regular Expression' option. You can save the result as a Named Query.