In zsh and others I could set EDITOR=subl -w. In HyperTerm I get:

Ignore the ugly glyphs, setting up a new mac and battling with fonts 😅
Similar problems when using Fish shell

Maybe this command should be invoked with a shell wrapper, to prevent any issues with custom configuration?
with zsh, I can set EDITOR=subl or EDITOR='subl' on hyperterm and iterm and have $EDITOR ~/.hyperterm.js work. export EDITOR='subl -w' fails with "zsh: command not found: subl -w" on both iterm and hyperterm, and sourcing export EDITOR=subl -w fails with .zshrc:export:64: not valid in this context: -w on both as well.
I don't think it's a hyperterm-specific issue. Hope this helps.
From fish:
➜ ~ $EDITOR ~/.hyperterm.js && exit
Unsupported use of '&&'. In fish, please use 'COMMAND; and COMMAND'.
fish: $EDITOR ~/.hyperterm.js && exit
This has been fixed since this, as it now executes bash -c 'exec env ${EDITOR:=nano} ~/.hyper.js'.
Most helpful comment
Similar problems when using Fish shell

Maybe this command should be invoked with a shell wrapper, to prevent any issues with custom configuration?