It can be done because I've done it.
To remove the good one, I would suggest using a pick tool to get the tongue started out of the retainer, and use some silicone lubricant to slide the pick tool between the lowest part of the tongue and against the retainer making sure that it isn't distorted. If it bends significantly (ie by pulling it up by hand) the likelihood it won't sit properly on refitting.
Make sure the tongue is spotlessly clean of any grit or crud, as is the retainer. Lightly lubricate the tongue with either red rubber grease or silicone spray, position the moulding so that the top curve is exactly in position, the start gently thumb the tongue into the retainer at one end regularly checking that the top corner will still sit in the correct position. Go easy on it and take your time exerting a firm constant pressure as you go round the moulding, and it will go on easily. You will feel when it slots correctly into the groove on the retainer.
There is a good chance that some of the bonding used on the windscreen fitment may be in contact with and support the retainer in part but don't be hamfisted and keep its profile as flat as possible when removing/ refitting and you should be able to do it ok