It is quite unlikely that your Pronto and TV lift will use the same RF codes. Your Pronto RF Transmitter sends 418MHz. A look at this
spec sheet seems to show the Venset uses 433MHz which is the same as the RU960 (Euro spec TSU 3500) so I don't think you'll be in luck.
Once I saw where the Venset is made I could have guessed the RF would be 433MHz. Almost 100% Euro RF is 433MHz so we are lucky that we can get our Prontos to control loads of home automation stuff.
There is an "ugly" solution to doing what you want. Look at these
. If you buy the Euro/UK spec 433MHz version (Amazon or Ebay maybe) you can use the part that turns the IR from your Pronto into the RF at 433MHz to control your lift. It is slightly complicated to set up, in that you have to first use the part that recieves the RF signal from the extender and copy the IR it ouputs from the original Venset remote. ie point the Venset at the RF to IR part of the kit and it will transform the RF into IR and you can learn that from it onto buttons on your Pronto.
Once you have learned those buttons you can put that part of the kit away and place the part that turns IR in RF in view of you Pronto and when you press the learned buttons it should control your lift because the IR from your Pronto will be translated into 433MHz expecting to be picked up by the reciver part of the kit, but rather it is picked up by you lift.
I know this works for RF power sockets as I used a kit like that for a few years before upgrading to a Bang & Olufsen remote which needed a completely different setup. The learning of the original remot took about 10 tries for each button, but I got there in the end.