Are Characters customized in different provinces due to dialectal differences?
Wikipedia has the following pages:

Sichuanese characters &amp; 四川方言字

Written Cantonese &amp; Cantonese characters

Written Hokkien &amp; 台閩漢字

Wu characters


Here you can find characters that solely belong to topolects.
There is also an introduction to topolectical characters:

方言字


Many topolectical characters are also still being prepped for Unicode encoding. If you're curious you can go through BabelStone Han PUA to get an idea of whats to come for CJKV extensions.
You will also notice that topolectical characters are not just simply written in simplified. Most historical documents are written in traditional and oftentimes the simplified characters that do arise are just simply 類推 (simplified characters by analogy).