You can set game rule commandModificationBlockLimit to a negative value with a command such as 

/gamerule commandModificationBlockLimit -999 

This doesn't make much sense, as you can encounter errors like 

Too many blocks in the specified area (maximum -999, specified 1) 

In my opinion accepted values should start at 1 (or 0).

You can simply set the maximum to 0 if you need this behavior.