I wanted to know if it's possible to disable the default index on Kibana dashboard or change the default page with a different one?
The default index can be changed in Settings -> Advanced.
If one isn't selecting you'll be asked to choose one.
If you want to change the default page, in
config/kibana.yml you can set kibana.defaultAppId to a different page, ie "dashboard".
There isn't a current way to disable having a default index but if you want to file an enhancement request with your use case you can do so at https://github.com/elastic/kibana/issues.