Yeah, as much as I dislike using spreadsheets for stuff like this, it does seem to be a “useful hack” that gets put into practice all-too-frequently.
Depending on how much control you have over the workflow, you might find it useful to create a new custom property to track “short name”. It’s relevance would be
(preceding text of first "." of it | it) of (computer name as lowercase)
This way, you get a lowercase version of every hostname, and no FQDN included. You can export a CSV mapping this short name to either the “real” hostname or computer ID, and do some Excel magic to map these to the spreadsheet list your CMDB is providing. Then you’d send your API actions based on the “real” name or computer ID resulting from the CMDB mapping instead of using the CMDB name directly.
If you’d like to pursue a tighter integration (for instance where BigFix updates the CMDB to reflect tge actual hostname, serial number, installed software list; or where the CMDB workflow can directly create BigFix actions, etc.) that is something we could help with in Pro Services, or you could engage one of the several partners who post about their integrations here. I understand there are some out-of-the-box integrations planned as well in the product roadmap.