Again, if the Supreme and XTend have the same firmware version, you can download the same application into both Supreme and XTend.
“They” are probably being silly and short-sighted there!
If “They” want a software development job done, then “They” should really engage a proper software developer to do it! (or get you properly trained to do it).
Why do people assume that “anyone” can just “do software”?
Would “They” hire a software developer to do an Instrumentation job?
If “they” want you to do this, then “they” should be budgeting (both time & money) to get you up to speed with it - you shouldn’t have to bust a gut over it!
If they can’t/won’t hire a permanent employee, your Distributor should be able to recommend a consultant to help you - they may even offer it as a service…