Dear Anshita,
I am not aware of any way to actually change the page text from the frontend.
One way would be to create a new entity with an unlimited string attribute that would be editable for user role ContentAdmin, but readonly for regular users. You could use a rich text editor from the Mendix Marketplace and display the HTML it creates on the pages. You’d have to create one object of this entity per page.
Not very elegant, but should get the job done.