No, I don't think that provides an open system.
There would be an option of voting for one candidate, which you would use as your candidate for the local MP, and your candidate by their party, for the calculation of proportionality.
On the other hand, there may be people who want to take the option of changing parties, changing candidates, so you would have a second part to the ballot, which I envisage being printed in slightly smaller type than the main ballot, that people could use to select a different candidate or a different party.
There is a question of their making a mess and choosing two things on that second one. Under those circumstances, if they were compatible, in other words if the person they voted for was with the party they'd chosen, that would be fine. Otherwise, that would just be a spoiled part of that ballot, and it would revert to their original one.
That's what I was thinking.