If I understand the requirement correctly you have a report that will contain several thousand account numbers and names of which you do not want to select 1053 of them for report analysis. Is that correct?
Monarch uses a 'filter in' process so we need to exclude those 1053 names from the selection.
The way to do this, since a very large filter statement would probably exceed system specifications, is to set up a filter flag.
You can do this my setting up a Lookup table. If you have only Monarch Standard or the list rarely changes you can use a lookup table. Compare the field value (say Account Number, Customer Number, whatever, Name is likely to be less reliable but possible) to the lookup table and if there is a value set a flag.
If you have a list that varies significantly on a regular basis AND you have Monarch PRO, then you can make the lookup table as a FILE somewhere on your PC or Network and maintain it outside Monarch. Use that file to perform an EXTERNAL lookup rather then an internal lookup. There is no difference to the lookup concept or the result, it's just likely easier to maintaining the list somewhere else if it regularly changes. I would give the task to the person who decides who is in and who is out of the filter.