The PD130 would kick out around 150bhp as the PD's are notorious for 'over-achieving' when it comes to power.
Most of the PD150's leave the factory with high 160's, mine was rolling roaded a couple of months back (as standard) at 186bhp.
Re-mapping is a term used to describe altering the manufacturers standard ecu settings for timing, fueling, economy, boost etc and modifying it to deliver more power.
Years ago this was referred to as 'chipping' (as a new chip would be hard soldered into the ecu) but now manufacturers software is simply modified or over-written. Plenty of people on here have had it done, with some great results.
In terms of the implications, obviously you're supposed to tell your insurance company. Many tuners boast their re-map are invisible, even to the manufacturers, so the chances of an insurance company finding the modified code are slim, but they do still exist.
Warranty, as above - if the manufacturers can't find the remap, they wouldn't be able to deny a warranty claim. But if they do, you will have a big argument on your hands to get them to pay for something they will argue was damaged by altering their product.
As for economy, most diesel drivers who have opted for a remap actually report an increase in fuel economy, which has got to be a bonus!!
I'd say if you can save that bit more, go for a 150. Better suspension as standard, 16" wheels over 15's, woody bits inside etc etc.