The problem with your plan is not with future flights; it will severely impact your current ticket.

Your bags will be checked all the way through to LHR. If you request to have them "short-checked" just to AMS, there will be a fee of €275 per bag in order to have the bags delivered to you in Amsterdam.

If you decide to simply not board your flight from AMS-LHR, your bags will be offloaded but will not be returned to you without a great deal of fuss and bother and delay - which will invariably involve paying either the fee of €275 per bag, or the newly-calculated fare for the open-jaw ticket you actually flew. This course of action also greatly increases the chances that your bags get lost, or are not returned for a considerable amount of time.

I would strongly advise you against simply "missing" your final flight; it will cause you problems with your luggage and will cost you a considerable amount of money, as well as time and hassle dealing with your luggage at Schiphol.

If you want to spend a few days in Amsterdam, then either:

• travel back without any checked luggage; in this case, you can safely miss your AMS-LHR flight, without consequences now or in the future, but you will have to arrange a new AMS-LHR ticket, separately and at an extra charge;
• arrange in advance that this ticket is changed before you fly, such that you have a stopover in AMS on the way home built into this ticket; this will require extra payment;
• plan a separate trip to Amsterdam at some other point in the future