Agree about a specialist, but probably moving an existing company into an umbrella structure is likely to be considered similarly to a sale for tax purposes.

In the UK, you have to specifically request HMRC to authorise any such plans if you want to avoid paying tax on it, and even then I believe it's only (relatively) simple if you're doing a straight share swap - so the existing company becomes fully owned by a newly created group company and the existing shareholders get the same allocation of shares in the new company. Anything else needs HMRC to assess the values of both companies and decide whether a taxable event has occurred, and what the nominal value to be taxed is. I'm pretty sure if you were trying to move an existing company into an offshore parent company, it'd be treated as a sale.

The mechanics of changing ownership under umbrella corporations is somewhat of a mystery to me, I have seen it done as part of a complex buyout of a small multinational.

However that was UK/US and some EU but non-german subsidiaries.

I suspect you are right about movement being considered a sale. My assertion was imprecise as I suspect it requires an upfront company layout, rather than post-hock.