You should be able to go advanced > add ( on master anyway )
Most of the options you mention are supported there at least.
Manually changing things is difficult, because you have to edit both the web files ( lua is hard but these are on the easier side ) and the init.d parser.... very difficult.
If an option is genuinely new / needed.... posting a feature request on the relevant ( github packages? https://github.com/openwrt/luci/issues ) site should be accommodated.
luci-app-openvpn is friendly in that way on the front end.... it's the backend and testing where odd options can be troublesome to implement without feedback from many.
I second the suggestion to use straight .ovpn files..... especially in cases like yours..... but notifying the developers is beneficial also.
If an option is genuinely new / needed.... posting a feature request on the relevant ( github packages? https://github.com/openwrt/luci/issues ) site should be accommodated.
I'm confused - there are no "options" because when you upload an ovpn file, you don't get provided options - you get provided a text editor that allows you to edit/add anything in the file.
This is if you uploaded an OVPN file using the "OVPN configuration file upload", not "Template based configuration". I have never successfully created a working configuration using the template based config approach. (I was trying to, for various reasons, create a tap VPN not tun, which could have been part of the issue.)
Adding ncp-disable was a matter of typing it in on a line in my ovpn file
Hmm... I wonder if the "OVPN configuration file upload" is only present in master and not 18.06 - it's been present in master for at least a month and a half, I've never run the 18.06 release
Someone commented that 19.something was recently branched into a release (release candidate?) branch, so that will probably have this new feature.