How do I replace specific tile with another tile?

I'm making a game that requires two different states of caves: one with a candle, and one without. With a candle it's bright inside, without it remains dark.

What I'm trying to accomplish:

"on start of frame", "if hasCandle=true", ...what here?

Is there a way to say "replace all using tile 1 with tile 7, all using tile 2 with tile 8" and etc?

You can do something like this :

[attachment=0:3aos9r1m][/attachment:3aos9r1m]

It's not mandatory to use the tileX and tileY variables, it just helps the readability by writing tileX instead of loopindex("x").