How to install a loading job via REST API call

currently, I only see the rest call to run a loading job, is there an API to install the job or it is recommended to install it manually beforehand?

Generally speaking, DDL, i.e. manipulating database objects (creating, altering and dropping schema, vertices, edges, queries) is done via either gsql command line or GraphStudio. It seems that the purpose of the REST++ API is DML, data manipulation only, i.e. upserting, modifying and querying data. A load job is DML, but creating the loading job itself is DDL.
So, long story short: no, there is no publicly available REST API for installing loading jobs. At least, I am not aware of it.
It makes sense, actually: external applications using TigerGraph should be concerned with data only (mostly getting – processes/analysed – data out). Admin stuff should be left to “official” tools.

Could an abstraction of this be done in installed custom queries. I might be way-off-base here but its a thought…

An abstraction is possible using a generic vertex and edge type, but performance will often be relatively poor and the queries can become a little hard to understand. It’s the equivalent of an EAV schema (for the relational heads among us).

Nevertheless I have used it for some specific use-cases.