Can you toggle finite blocks in Minecraft Creative Mode?

If you just want this for a few specific types of blocks, you can create a scoreboard of type used:<block_ID> and then run the command clear @p <block_ID> 1 (and reset the score) whenever this score is 1.

No, but you if you're open to running a server (but only playing locally), you can:

1. Start up a Bukkit/Spigot Server
2. Install Essentials (there's lots of variants out there, doesn't matter which one, as long as it works) and WorldEdit.
3. Run // (on a bare hand) to instantly break stuff (from WorldEdit)
4. Run /fly to let you fly in Survival (from Essentials)
5. Just /give, /i, etc. the items you need (from Vanilla and/or Essentials)

You can take damage (except fall), insta-break, fly but anything you need has to be spawned in using the /give command and stuff is finite.

This was pretty much the old form of Creative before Creative Mode was even a thing.

You can use the /fill X Y Z X Y Z Minecraft:[block you want to fill with] command for up to 32768 blocks at a time. Simply point your cursor at the block you want to select and use the tab key to auto fill co-ordinates - 3x tab for full co-ordinates (X,Y,Z). I use this all the time when building large scale, you might also find it useful. One advantage is that you don't need to have the block you want to fill with in your inventory.

No, you are unable to toggle finite blocks in Minecraft Creative Mode; however, despite being very difficult to set up, this is possible to implement with commands. I don't think anyone would really try to do it though.