Yes, with one important condition: enable Preferences → General → Auto Save.

In the current v0.19.1 code, an external file-change event is reloaded immediately when Auto Save is enabled and the open tab is currently saved/clean. If the tab has unsaved local edits, MarkText still shows the confirmation bar so it does not silently overwrite them (v0.19.1 source).

So the behavior is:

• Auto Save on + no local edits → reload automatically.
• Auto Save on + unsaved local edits → ask before reloading.
• Auto Save off → ask before reloading.

Auto Save is documented as a Boolean preference, disabled by default, with a configurable save delay (preferences reference).

There is not currently a separate preference meaning “automatically reload external changes but do not enable Auto Save.” If that is the exact combination you need, it would require a feature change. The unconditional form would also need a defined conflict policy for dirty tabs; automatically replacing those would discard local edits.