Copy MyTag to comments - How do I do it for just a few files?

Dear Pioneer-Community,

I'am heavily dependent on a Rekordbox feature which copies the "MyTag" string of a certain music file (m4a format) to the comment section of its file. Right now I'have reached a point where I am having problems to make it work more conveniently.

The mentioned feature is located in: preferences > advanced > browse > "My Tag: Add "My Tag" to the "Comments". 

As I am importing new tracks into rekordbox I usually tag them right away to keep the whole thing in order. Afterwards I need the string of "MyTag" copied to the comment section to work with iTunes. Therefore I activate the feature "'Add "My Tag" to the "Comments'". This usually takes minimum 30 minutes for rekordbox to copy.

If I decide to add new tracks I have to deactivate the feature only to activate the feature again, making rekordbox work on the whole library for another 30 minutes. 

I don't have an enormous amount of tracks nor do I have a slow macbook. But this whole ordeal is making me wonder if there is a faster and more professional way to do this in rekordbox.

Does somebody know a way to copy the "MyTag" content to the comments only for some files and not the whole library? 

Thank you in advance.

Rekordbox version: 5.0.3. 

Running on a 10.11.5 OS X Macbook.