The full blockermans-projectile-workshop.zip includes a ui file under project/ui.del, which can be compiled with OSTW. Otherwise, check the workshop.codes description for a UI code.
ui.del provides a way to test out ProjArg changes in real time, with specific instructions included in the mode itself.
Want to start off with pre-set ProjArgs? Paste them in this rule, such that Event Player._projArgs = <yourProjArgs>;
Second action is my pre-set ProjArgs.
Yes it's laggy (as of v1.0), no I don't care rn because you can still use it for its intended purpose of trying out changes to ProjArgs live.