No, it's a tricky splice to carry out - especially around something like a thimble...but it's interwoven through itself and cannot come apart. You have to see it to appreciate it.
Is this a good method to try this knot?
http://www.precourt.ca/brummel_splice.pdf I haven't seen that tutorial before - but yes, that is a good one to go by. The Samson Rope tutorials have some additional detail regarding tapering and a way to do it without unstranding the line...personally, I put the line on a table and cut it with a razor blade at a high angle to get a taper on the tail. It's not as perfect or as long a taper as picking and cutting out pairs of strands but for what we use this kind of line for (small control lines), it's fine.
