Not really a no-no. In fact you have a better chance of fitting all these extras to your car than I do in mine as it seems Peugeot pre-wired the first 2 years of D9s for most optional extras.
Here's a list of things to check:
Drop fuse panel & look here:
If you have the little white plug shown here, that's where the cruise control stalk plugs in. 2 torx bolts under the headlamp adjuster/diagnostic port allow that to come out & you should have something plugged in between the 2 - that's where the on/off switch for cruise goes. Here's mine (which doesn't have it):
Prise up the coin holders with a screwdriver to the rear of the airbag switch in the centre console - if you have a load of plugs plugged into the coin holders, you're ready to go for heated seats.
Look under your front seats - if you have a red & yellow plug taped up in the corner nearest the door, the yellow plug is your ticket to fitting electric front seats.
Chances are, the wiring will probably be there for the trip computer too if you have all that. All you need then is somebody with a PP2000/Peugeot Planet clone to activate them on your BSI.