But if the amount is significant, and the existing buttonholes are either past the new length, or right on the edge, then removal is the better option.

Always discuss the options with the person who owns the jacket BEFORE anything is done.  My client wanted me to put new buttonholes on, and I refused.  I use a standard domestic sewing machine, and my buttonholes are not that decorative.  I think it would be unprofessional to try and put them on.  So I would rather NOT alter the jacket then sew my buttonholes on.  I think I know best.  After all I am the expert.  Not the client.

But I discuss options.  Take the b'holes off but put the buttons back on.

I have mentioned in the past a manufacturer who decided that standard buttonholes were the way to go, and that they should be cut.  If you have ever done  clothing alterations, you will know that cut buttonholes are a nightmare.  Again I would rather not touch the jacket.  I offer solutions.  Raise from the sleeve cap - BUT it must not make it too tight at the upper arm.  If the person is a male who works out and has big biceps, this may not be a good option.  Covering the buttonholes is another one.  If it is a black jacket, use black satin.  This can look great.  So there are options.

But in the meantime, here is a quick way to unpick.  I did this video to replace one I had created previously, because this jacket was light in colour and made it easier to see what I was doing.

Happy altering
Judith Turner