Can we mandate the locking feature while loading any file in RTC SCM

In RTC, you can require pessimistic locking at the stream level.   In particular, if you specify that pessimistic locking is to be used on a particular stream, then pessimistic locking is enforced on every repository workspace that has that stream as a flow target.   When pessimistic locking is specified for a repository workspace, when the file is loaded into the sandbox, it is loaded read-only, and is made writeable when the user successfully "locks" that file for update.  So there is no "pop-up for lock" when the file is loaded, but rather when an attempt is made modify the file.   Also note that the editor needs to understand the "locking" protocol ... all Eclipse editors understand it (and I believe, all Visual Studio editors).   If you have an editor that does not understand the locking protocol, you will just get a "file is read-only" error, and then you can use the command line or some other mechanism that does understand the locking protocol to lock the file (which makes it writeable).

 For all I know RTC is not built foe pessimistic locking - the schema you describe - The configuration is based on some extensions. So my answer would be no.