Hello, I added .htaccess with rule to disallow execution of .php inside these Wordpress directories:
wp-content/uploads/
wp-content/themes/
wp-content/plugins/


Can it cause any major issue?

update after 3 weeks: i did not found any big issue, only i found very rarelly that some plugin function (example generating captcha image) stopped working. But this can be easilly discovered by reading error_log file, always when such malfunction happpen, there is an entry mentioning that "Access was denied by Apache configuration" and file path. So one can see and remove execution restriction rules (from .htaccess)