how to customize admin group permissions in aem?

Hi @karthick1356, you should not modify OOTB admin group. If none of OOTB groups meet your requirements, you should create new custom group with proper set of permissions. Regarding customization/restrictions of permissions that are inherited from admin group  - technically this will be possible, but it will mean you have to use Deny rule which is against good practices - you can find full list of good practices for user and groups  under 

https://experienceleague.adobe.com/docs/experience-manager-65/administering/security/security.html?lang=en#best-practices