How can I convert an NSDictionary to an NSMutableDictionary?

In case of Swift

var tempDic: NSMutableDictionary = yourDictionary.mutableCopy() as NSMutableDictionary

Use -mutableCopy.

NSDictionary *d;
NSMutableDictionary *m = [d mutableCopy];

Note that -mutableCopy returns id (Any in Swift) so you will want to assign / cast to the right type. It creates a shallow copy of the original dictionary.