How do I change the presets of dynamicText

If I am understanding correctly, you are trying to get rid of the default #timecode# being loaded when starting a new Text:Simple filter.
2022-02-06_05-06-25

You can edit the (defaults) file in DynamicText, but it does not change the timecode from being inserted.

You could make a blank preset, but it would be set to the current Video Mode resolution size at that time the preset is made.
2022-02-06_05-14-13