There a several ways to rig overloaded track selection.

1) MPC-HC - Options - Internal Filters - Splitter - Subtitle Selection Mode - Advanced.
There is a link to syntax manual, but you probably want either "*:eng|d;*:eng" or "*:eng|n;*:eng" (without qoute marks).

2) MPC-HC - Options - Subtitles - Misc - Ignore Embedded Subtitles.
Autoload folder is set on the same page. Relative path to subfolder near the video begins with a dot, absolute paths begin with a drive letter.
Extract the track you want (e.g. using "Inviska MKV Extract") into any autoload folder.

3) MPC-HC - Options - External Filters - Add - ffdshow raw video filter, after adding double click it for settings - Show / hide filters - Subtitles, where you can add another autoload folder for a secondary track, e.g. in another language.

There are sometimes subtitle tracks that look unreadable in either internal renderer or ffdshow, due to overengineered effects, or bad colors, or not playing well with font overrides and going offscreen, so you can swap chosen tracks between their autolad folders. I like to override subtitles half-transparent, for example. YMMV.

When I have unwanted issues with default tracks I just modify the headers and don't look back.