Upvote:2
Although there is no clear policy on this, the general consensus is that this will not be allowed unless you have a long layover in London (>7/8 hrs).
This is due a number of factors:
To make 'Hidden-City' Ticketing more difficult - Often certain city pairs price out cheaper than the interconnecting points.
To account for Operational changes - if BA for any reason has to reroute/cancel your flight, they may leverage partner connections etc to get you to Paris. In this case they wouldnt want your bag only tagged to LHR.
Some suggestions:
Is your rebooking fee high due to the fact that your ticket is non flexible or due to the fact that the airfare is higher when re-calculated solely to London? If you are actually on a flexible/semi flexible ticket, I would consider rebooking only the London-Paris leg to a later date (even many weeks in the future if that produces a permissible fare). This will enable your bags to be tagged LHR only. Another approach would be to try rebook your London-Paris segment from one of London's other airports (City, LGW) whereby you have to claim and re-check a bag yourself. You could discard the London-Paris segment.
The view is that it is generally at the discretion of the agent who is performing your bag check and/or their supervisor. If you can come up with a compelling reason why you need the Bag at LHR you may be able convince them to short check the bag (certain items you have got in the US and have to provide to a business associate that you are meeting at LHR etc.)
Make alternative arrangements for getting your bag/contents to London (courier light but bulky items etc)