If you elected to load the project without its subunits, you can later load individual subunits: Right‑click the subunit in the browser to display the menu and select Load [unit name], or select Load [unit name] with Subunits to load the unit together with all its subunits.
To unload a unit, right‑click the subunit in the browser and select [unit name].
Units that are not currently loaded are indicated by (U) before the unit name in the browser.
If you do want to unload a unit, but you want to prevent it from being loaded the next time you open the project: