The fact that you are having this problem indicates that the threads of the inner will be damaged quite badly when all is said and done. I had the same thing happen and had to use a lot of heat on the outer tie rod end to even get it to make one turn at a time between heatings. The end result will be that you will be able to thread the new outer tie rod end on easily, but that it will have a wobbly loose fit on the inner's threads. this will make it difficult to lock on the jamb nut without pushing the toe alignment out, and also provides a weak connection to the steering rack due to reduced thread height.
On the self locking feature of these pieces, I used 1/4" drive sockets on them as they tend to be able to stay on the self locking feature until there is just enough of the lock nut's influence on the need to use the self locking feature, and when the socket falls off, the threads have just become clear of the nylock insert's grip.