There isn't any benefit to applying a stain now that your house has been painted. A stain has to penetrate into the wood and the paint will stop that from happening.
If you want the stain back then you will need to strip off, remove, all of the paint. This will be an enormous amount of work compared to maintaining the existing paint. At this point it is economically better to remove the loose paint, spot prime with a good primer and repaint.