One way to this is to use sets (this is the simplest as it doesn't require Sub-Category in the VizLoD in order to calculate the Top 10).
So first I create a set from Sub-Cat
Then I set up the set as follows
Once we have this, I can create the following calc
[Top 10 or Rest]
IIF([Top 10 SubCats],[Sub-Category],"Rest")
and then use this as my colouring in the Pie. I've also added a [Top 10 or Rest - Sorting] calc (very similar to the above one), so the "Rest" appears last in the Pie when I sort it.
One other thing to note (like FIXED LoDs) due to the "Order of Operations" sets are calculated before any "regular" filters are applied. As such if you want the top 10 to be responsive to filtering (say by selecting just a single year) you need to make this a context filter (this bumps it up the calculation pipeline)
Hope that helps, and makes sense, but let me know if not.
Top 10 and Rest pie.twbx 1.2 MB