Is there any code difference between SQL Developer edition and Standard edition.

Thankfully, code that runs on Developer Edition will also run on Standard Edition. There are very few surface-area feature which are Enterprise/Developer Edition only.

However, code may run in a different way from the point of view of performance, since some optimizer and performance features are not available in Standard Edition. This may be something you don't notice, but you can also be severely burned.

You can find a list of differences here: https://learn.microsoft.com/en-us/sql/sql-server/editions-and-components-of-sql-server-2019?view=sql-server-ver17, but I don't think this list is complete.

A great piece of news in this area, is that the upcoming SQL Server 2025 comes with a new edition: Standard Developer Edition, which removes this pain point. Not that this is going to help you today, but I still like to mention it.

the reverse is true. SQL Developer has all features of Enterprise (with scaling limits).

You shouldn't face issues with a change from Standard to Developer in that you are increasing functionality and removing any limits on Standard since Developer is the same as Enterprise, just for Development.

Second question is the same answer. Because you are going up in Edition, you will not see anything that runs in Standard Edition that will not run in Developer. You are good on this one.