A button or an input field should have different access right
It is described in CP600 help - Security.
I don't know how it works with guest user. I did it like follows:
Use only 2 users: administrator and operator
1. Define UserGroups -> operator
2. Mark Use last visited page for user groups operator and admin
3. In Authorization Settings of user group "operator" open "Diag" sub-folder and find your input field (check exact name/number of the field from Screen->ObjectView when the element is selected) and set to "Read Only"
4. Define user Operator. Make user Operator member of user group operator
5. Set the user Operator as Default User (only one default user is possible, unselect admin)
6. Set password for user Administrator. Set Logoff time 1 min for administrator
7. Set Change Initial Password to False for both users
8. Right click on Security folder in ProjectView and select Enable
9. Download the project, switch off and on the panel
The procedure is pretty difficult.
I found that in case you need to change some settings from above, concerning security, you should change it, disable Security (item 8), download the application. Then Enable Security (item 8) and download again
Default password for admin is admin
Good Luck !