Can files be set to readonly permission after scm load?

Note that these actions would not cause the files to be loaded as read-only in the file system.

Thank you Kim, however I am afraid what Geoff said is true, it will not cause files to be loaded as read-only in the file system. We need to load file in read-only format.

No, RTC currently provides no way to specify that a file in a sandbox should be loaded as read-only.   You can specify that in a given stream, a change to a given file (or to all files in a given component) cannot be delivered, but you cannot specify that a file in a workspace is read-only (i.e. you can always checkin changes to any file that you have read access to).

Thank you Geoffrey for confirming such function does not exist in RTC. Users would like to know if API level source can be modified so that when file load is completed, custom followup action can be performed to change permission of files.

I do not believe that the load functionality in RTC is suitable for customer extension.

Note that work item 93617 (pessimistic locking) would load files as read-only but wouldn't provide read access control, because anyone can checkout a file (that isn't already checked out).   So whether this would be useful would depend on why you wanted the files to be loaded as read-only.