Yep. They might pull faces at you, but there is nothing other than tide timings stops you over-nighting in Preston on the way up - although I usually recommend to people they hang a left on the way down off the Ribble Link and go to Preston anyway.
If you go up to Preston and then leave there on your way to Savick Brook, Please Please let both CRT and Riversway Port Control know *in advance* that is what you are doing. It saves them having to scramble the Lytham lifeboat to try and find you ...
It's probably one of the places that should have been on the IWA Silver Propeller list - hardly anyone goes there, but it's a great little (40 acres in a city centre!) marina and dock basin.
It is also the "safe harbour" cop out if you fail to make Savick Brook in time to clear the rotating sea lock cill, but you do need to pay a tenner a night for the privilege. If that's too much, make sure you moor on the bullnose outside the marina - on the floating buoys please! - and not on the riverbank. The Ribble has the second biggest tidal range in the UK - up to 8 M / 26 ft - so you really do not want to be over the deep mud on the riverbank when the tide goes out!