Worked it out.
If anyone else needs anything like that, its a bit hacky but it works:
a screencap of the input mask:
what i put in “Value” (all one line): </none></phone-settings><uploads><file url="https://192.168.210.5:1443/voipphone001.ionicon.local.tar" type="certificates_8021x"></uploads><phone-settings><none>
what the resulting config line looks like (all one line): <none perm=""></none></phone-settings><uploads><file url="https://192.168.210.5:1443/voipphone001.ionicon.local.tar" type="certificates_8021x"></uploads><phone-settings><none></none>
Edit: Any entries below this will be ignored, so delete it and reapply to the bottom if you add something else afterwards.