h-4 based EAD can it be got after primary H1-b holder switches job

[testytesty]

Hello,

I have h1-b valid till Jan 2017, with approved I-140 from the current company, could i change jobs now? and will I be able to apply EAD for my spouse who is on H-4 later?

On the other hand, if I apply and get her EAD before switching the job, will it be valid only till Jan 2017, and what would happen beyond that? will i be able to apply for extension after that?