I'm pretty confident that you'd be able to switch if you so desired but I haven't heard from anyone who has tried.
Dear JJ1000,
Thank you for your recent inquiry regarding this British
Airways credit card account.
The enrollment incentive associated with the application
you completed is for a total of 100,000 bonus Avios with a
$95.00 annual fee. You will receive:
* 50,000 bonus Avios after the first purchase
* 25,000 bonus Avios after $10,000 in purchases within the
first year
* 25,000 bonus Avios after $20,000 in purchases within the
first year
Unfortunately I am unable to honor your request to receive
a $75.00 annual fee and the additional 50,000 bonus Avios
upon the first year anniversary instead of receiving
25,000 bonus Avios after both the $10,000.00 and $20,000
spending thresholds. I apologize for the inconvenience
that this may cause you.
If you have any further questions, please reply using the
Secure Message Center.
Thank you,