Put newcommand tex file after newcommands in main tex

[Turgon-Aran-Gondolin]

Is your feature request related to a problem? Please describe.
When I use preview feature, I found the commands I defined in the newcommand tex file got overwrited by the newcommands from the main tex file. This cause the preview to be unstable, even break down in most cases.

Describe the solution you'd like
Add the new command tex file after the new commands from the main file, but before the actual math environment. This way I think I can define newcommand in the global new command file to overwrite the ones from my main tex. I don't know if two conflicting new command definition will cause further problems.

Describe alternatives you've considered
I don't have another idea to avoid the conflict between these two.