Gail,
my understanding is that as the stoma (the area that the tube goes through from the surface of the abdomen to the stomach) heals the two begin to grow together. once it has been in 6 weeks or so they have healed enough that as long as you get a new tube in fairly soon (like within a few minutes) there should be no real problem.
No matter what however, you should always follow doctor advice. Whenever my son or MIL get a new "appendage" or appliance I make sure to ask the docs what I should do if it fall out, has a complication I do not understand or know already how to deal with, etc. Thankfully we have never had a problem that wasn't fairly easy to fix.
Heidi