EB1 GC i-140 passed and switching company

[JNJOE]

Hi,

I'm currently in L1A visa and Working for Company "A". The company have applied my GC under EB1, my I-140 is passed. I read from blogs that it may take longer than expected to get the EAD/green card for EB1. 

Now my question is

1. Can I switch company with my Approved I-140 and do the rest processing with the new company?

2. If no, how long should I wait to switch company?

3. Will I get an Extension on my EB1 if the EAD/GC takes time (as in EB2 category) if I switch the company?

Note: My current L1A expires in 1 year

4. Will there be any additional paper works to be done with USCIS when switching the company (I-140 passed stage)?

Thanks

Joe