This Submod wllows you to change the blink speed as well as disable it all together in Monika After Story.
Simply extract/copy the files into your MAS and it will install everything.
Open blinking-speed.rpy to change speed or simply open your console and change the store.persistent.mas_blinking_speed value to the desired speed. However for either of these you will need to reload your MAS.
Delete the game\User-rpy\Baaa Mods\blinking-speed.rpy and replace sprite-chart-20.rpy and sprite-chart-21.rpy with original copies