Hello Paul
By default, whenever you create access lists, whether standard or extended, if you don’t include sequence numbers in your statements, by default each statement will receive a sequence number with increments of 10: 10, 20, 30, 40 and so on, as you stated in your post.
This is done so that you can more easily edit access lists, by removing statements by specifying their sequence number, or by adding statements using sequence numbers in between the existing sequence numbers. You would add and remove statements using the ip access-list standard/extended command as you mention.
The CLI gives you these capabilities, however, I find it somewhat easier to use the other option that Rene states, which is to copy and paste the ACL into a text editor, make sure everything is in order as you want it, and then just paste it back into the CLI. However, different things work for different people, and only if you try both out will you determine what’s best for you.
I hope this has been helpful!
Laz