Advice on copyright please!

I would like a bit of help please. You've probably answered this question a lot of times.
I am an amateur composer who wants to publish my music. I don't want to make any money out of my compositions I just want to ensure that it' can be performed by anyone, professional or amateur. I don't want it changed or modified though, except for minor changes, if individual musicians want to change the dynamics, say.
Using the licence chooser, Attribution-NonCommercial-NoDerivatives 4.0 International is suggested.
My concern is that this is irrevokable and I'm not sure if that paints me into a corner in some way?

Are there alternatives?

It's a subject that should interest us all on this site, even "starving musicians" because, you never know, they might just come up with something steal-able!  I don't trust anything once it's on the web either even if it seems it can't be downloaded. Any music can be downloaded if your computer/phone has a earphone socket. 

However, I'm in the UK. You don't say in your profile where you live so the following is general about copyright and applies to the UK and associated Performing Rights societies elsewhere.

https://www.prsformusic.com/works/how-copyright-works

Know for a start that you always own the copyright unless you sell it or give it away (which should be supported by documentation).

The question is what protection do you have?

So I'm with PRS. I do what the first paragraph suggests - mail a copy of the file (for me, a score of sorts and a recording) to myself special delivery. Then I register the work with the Society for such protection as it offers. The fee is a one-off £100. 

Unless you're about to get a broadcast or recording offer, it's probably enough to send yourself a copy of your work making sure it bears your name and a timestamp of some kind. This is ultimate legal proof. But on no account open it. Keep it safe. It's meant for opening under the eye of a court if that ever proves necessary.

If you're in the UK there's useful stuff on the site including the gubbins on Copyright Law.

= = = =

I had a look at the site you mentioned but couldn't make much sense of it.  It seemed to be telling me more about what its hopes are and what it does for itself than how it protects your music. I couldn't see if a membership fee was needed.

Looking at the licence itself :

https://creativecommons.org/licenses/by-nc-nd/4.0/

it doesn't seem to offer the sort of protection I'd look for but I've only glanced through the site. I couldn't find where to join or register your work. You may need different arrangements for different works. 

As I say, it's probably enough to post your music to yourself now; and make sure whenever you load it onto the web that you set the permissions.

Best of luck.