It sounds like you're trying to change a setting that is defined in the search app. Know that config files are processed in alphabetical order by app name so 'search' will take precedence over a later name such as 'thisismyapp'. The solution is to change your app to come before 'search'.
You can use
splunk btool --debug props list to detect this situation before restarting Splunk.
Thank you for your reply.
The name of my app is before the search up, but that it's still now working.
Any other idea?
What setting(s) are you trying to change? Have you used btool to see where the setting is defined?