Office relocation

Hi guys, so I will be joining a BB in Hong Kong as a first year analyst next summer. I grew up in the US and have families in the UK. I only picked Hong Kong as the destination for my internship for the international experience. Therefore, I still want to come back to the US or maybe UK when I get a chance. I’m wondering:

1. How easy is it to relocate to a different office?

1.2. If it is hard to do a transfer within my BB, how likely is it to jump to another BB in the US?

2. When is the best time to do so (i.e. year 2 analyst? year 1 associate?)

3. Which group makes the easiest transfer?

4. Anything else I need to prepare for the transfer?

Thanks for your time in advance!