How to copy old world into new world, y -4096?

[MatyasP]

How to copy old world into newer world (not as parts "schematic" as in WorldEdit) to lower level of Y axe (-1024, -2048 or -4096)? Map backend: sqlite3 (old world: old schema, newer world: about month after migration to new schema)

Could be day light in lower level? What I need to do for it?

My idea is:
1) Old world is in old DB schema. I must migrate it into actual schema (I must do it through levelDB between two sqlite3).
2) Import table from DB of old world into newer world under different name
3) Change integer of Y coords in table from old world +newY with SQL command
4) Import data from table of old world into table of newer world OR merge both into new table
5) Save DB and use it
Is this right way? What more I need to do? What is optimal newY (-1024, -2048 or -4096)?

What about AdvTrains - how to import AdvTrains railway net from old world to newer world with change of Y coords?
And datas in signs (basic_signs, display_modpack) etc. - are they saved in blob of worldblock data or I must do for it too something more?

Thank everyone that help me!