Take a look at the email with template module. There you add the possibility to add tokens to your text which will be replaced with data when you use them.
If you do not want to send mail you can only use this object to create the textstring and after the token replace copy the text to some other object and delete the mail object. If you only want to change some text in a form you can also use the formatstring widget https://appstore.home.mendix.com/link/app/264/Mendix/FormatString
The token functionality is exactly what I am looking for within the rich text editor/viewer. However I do not want to send an e-mail. I want to display a text in the application which is managable for the administrator. I do not see how to use the email with template module as a solution for my problem. Have you used this module in such a way before?