josan420
It depends on the methods and capabilities of the developer who is customising the code.
It's a difficult task to manage any complex application if you want to go your own path with customisations and also take the advantage of the new updates.
Generally, the guys who purchase the extended license goes their own path and never merges with the new release we provide. Or looks into the source and if they like the feature they try to copy/paste the implementation.
In short, it is difficult as you will have to code compare all the files with either GIT or tools like winmerge.
For example if you are currently in 3.4 and start customisation. And during your customisation phase we release new updates for 3.5, 3.6... 4.0 then when your site is live, our current version might be 4.0
Then obviously you will wait for your business to start and after few months you would want to update, at that time we might have already released 4.1,4.2... 5.0
Which will have massive changes.
