Is there a way of reusing existing load case definitions across different jobs?
I am thinking here of situations that require many load cases to be set up to define a selection of operating conditions and then another set of load cases to process those OPE cases into meaningful results - say 5 different temperature cases + installed @ ambient requires 15 algebraic load cases to be set to determine the EXP stresses
Can I somehow take the load case definitions from a previous similar job and reuse them in the new?

There is no built-in method to share load case definitions between job files. However, the static load case data is stored in the _J file. When you start a new job, for which you want to utilize predefined load cases from another job, copy the existing _J file (for the old job) to the new job.

Then when you start static analysis for the new job, just ensure the loads and the load cases are setup properly.