It is not possible to do this at runtime. Microsoft's Raymond Chen answered this very question a while back in his blog (https://devblogs.microsoft.com/oldnewthing/20170906-00/?p=96955):

Can I enable Large Address Awareness dynamically at runtime?

... Unfortunately, there is no way to change the setting at runtime, nor is there an override in Image File Execution Options. The value in the header of the executable is what the system uses to determine whether to give the process access to address space above the 2GB boundary.

So no, this is hardcoded in the executable header. He then goes to suggest the two-executable (and maybe a loader/chooser) solution, similar to what's suggested by @PeterCordes.

Alternatively, since this seems to be strictly a fallback scenario in case of any issues - maybe patching the executable header in field is an option (as opposed to changing config in field)? See How to make a .NET application "large address aware"? for pointers on how to do that.