Hi Gareth,
Yes you are right. If you created a a sensible walk pattern using the exits initially created in the Location Editor then the character will not deviate from that pattern during the game even if you open up a new exit in a room where that character is.
However a random moving character moves according to the latest exits available in a room so might feasibly use the newly opened exit and move through it. Same if a Character is set to 'follow you' and you go through a newly made exit - it will follow you through.
But remember you can change/rewrite the state of a walk pattern during a game using the "pattchar" actions
pattcharn1=X$
pattcharn2=X$
pattcharX=Y$ - change a move pattern of a Character
eg: pattchar1=random ; pattchar3=p,p,p,2,1 ; pattchar2=static ; pattchar16=follow
Also you can enter a special pattern for a random moving character to prevent or prohibit it entering location(s) by creating a pattern in the Character Editor move pattern field eg:
x13x15x
(Char can move anywhere except by any exits leading to rooms 13 or 15)
If you change a pattern to say:
pattchar3=x56x
It means that character will now be set to random but it will be unable to enter location 56.
Hope that helps.
Phil.