Thank you everyone for your excellent replies!
By cobbling together all of your replies and some other various information, I've managed to write a simple bit of code that will do this.
Ruby:
$gameMap.event(this.eventId()).setImage($gameActors.actor($gameVariables.value(n)).characterName(),$gameActors.actor($gameVariables.value(n)).characterIndex())
That looks complicated, but it's not so bad.
Let's break it down
Ruby:
$gameMap.event(A).setImage(B,C)
This is the basic function itself (Big thank you to
glaphen on that one). Here,
A is the Event ID of whatever event you're trying to change, and
B is the filename where the image you'll be using to replace is located, and
C is the index within the file of the specific image (Thanks to
Eliaquim for that explanation).
This is what you can use to determine the event ID (
A) of
any event, meaning that you can just copy this script into whichever event you want to use without manually finding the Event ID, or you can even use this in a Common Event (which I would highly recommend, as it will simplify your life greatly)
Code:
$gameActors.actor(D).characterName()
This returns the filename (
B) for the image you want to use, where
D is the Actor ID you want to use.
Code:
$gameActors.actor(D).characterIndex()
This returns the index (
C) within the file image you'll be using, where
D is the Actor ID you'll be using.
This is just a snippet of code that references the n-th variable, which I used to determine/select
D. You always want to use the same variable number, but which number specifically used makes no difference. For instance, I used the variable 0006. You'll need to set the value of this variable appropriately, probably using another bit of code, or a common event.
In terms of setting the value of whatever variable you're using to something actually useful, you can use the "Control Variables" event command with the following script.
Code:
$gameParty.leader().actorId()
This will return the Actor ID of whoever is leading your party, to be used as
D to define
B and
C.
I think that's pretty much the whole of it. Have a good day, or evening, or whatever time it happens to be.