For both the MUX effect plug-in version as the MUX synth plug-in version you can setup a MUX preset file that must be loaded whenever you plugin MUX Modular:
For the effect version: Save a "Startup Effect.Mux" in your user/library/mux sub-folder.
For the synth version: Save a "Startup Synth.Mux" in that same sub-folder.
Note: Don't save it as a FXP (=VST file), save it as a MUX file using the Save As button in the MUX editor itself.
Then navigate to your MUX folder /User/Library/Mux then click New File and enter "Startup Effect.Mux" or "Startup Synth.Mux".
You can use the "Edit VST Initial Delay" function in the top level Modular Area's options menu to report a VST delay time to the host so that the host can apply APDC (Automatic Plug-In Delay Compensation), if it supports that.