Source code management - Subversion

Regards

before i want say than my knowledge of smalltalk is poor; and my knowledge of Smalltalk tools not exists :)

I´m used to use source code managers in another languages for handle text files. In that environments when I "unprotect" a file nothing more can write on it. I understand the equivalence of that in Smalltalk could be a "check out" to method level, or class level. Exists something like that in Pharo/squeak? Monticello could be work of that way? Imagine for example I want unprotect a class of Monticello server code; nobody could change that class , but is possible for another developers change another classes or methods. I don´t know if explain good...

Thanks for the help.