If you have a dashboard that has a panel with a search like the one below:
| rest splunk_server=* /services/-/-/admin/......../appName/local
| table name splunk_server title
How can you make it so that it searches the other search heads? (a search like the one above returns values for the current search head and its peers - indexers)
If you want to search from other search head you must define those as a search peers to this node. Usually this is not a thing you want to do as it’s affects also on all normal searches.
If/when you have a MC (monitoring console) it has defined those SHs as a search peers already and you can run that query there.
If/when you can set authentication&authorization to that command and use it in custom command it should work. I don't see any (real) reason why you couldn't use python and make rest request from it to correct target?
If I recall right in splunkbase there is already some package for doing rest inputs (TA-rest or something)? Probably you could use it as starting point if it didn't work without changes?