403 forbidden when changing settings on WP Multisite non-main sites

I had the same problem – I found the rules in Apache modsecurity that include a set of exclusions for WordPress didn’t cover /network/site-settings.php, so I could do everything except edit sites in my multisite setup.
In the file /usr/share/modsecurity-crs/rules/REQUEST-903.9002-WORDPRESS-EXCLUSION-RULES.conf I added the following lines:

SecRule REQUEST_FILENAME "@endsWith /wp-admin/network/site-settings.php" \
   "id:9009999,\
   phase:1,\
   pass,\
   t:none,\
   nolog,\
   ctl:ruleRemoveById=941140,\
   ctl:ruleRemoveById=941160,\
   ctl:ruleRemoveById=942190,\
   ctl:ruleRemoveById=942240,\
   ctl:ruleRemoveById=942240,\
   ctl:ruleRemoveById=980130,\
   ctl:ruleRemoveById=949110"

…it’s my first experience of editing modsecurity rules, so there is probably a better way of doing it – but it worked.