Moodle only looks for database install stuff for (some of) the predefinded types of plugin - and the way it processes database install actions is the same for all types of plugin.
If what you are trying to do fits into one of these standard types, then you are strongly recommended to make a standard plugin type. It will save you pain in the long run.
However, if all else fails, you can use Development:Local_customisation.
General plugins
how to generate new tables
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