"Blocked" might be a little overly simplistic.  While it's certainly true that a hardfork is less likely to occur if there is a lack of either adequate hashrate or adequate economic activity, you can't technically "block" a fork on any scale.  If you really wanted to, you could modify a full node client and fork yourself off the network right now.  No one can stop you.  But at the same time, no one would care if it was just one person.  It's a matter of how many people decide that a fork may be viable and how strongly they believe in what they're doing.

The real questions are:

How many nodes and miners are enough for a fork to survive at all and do you have them in sufficient quantity?  And if so, would survival alone be worth the effort and risk if all you've really achieved is the creation of an altcoin?  Or if you have your goals set a little higher, how many nodes and miners are enough to build the longest chain and do you have them in sufficient quantity to change consensus and form new rules for the network to follow?

If you do have the numbers behind you, no one can stop you.  If you don't have the numbers, still, no one can stop you if you really wanted to, but it probably won't be worth trying.  There is no "blocked", just a "risk vs reward" assessment to consider.  Although it's generally considered that a united chain is more rewarding than two split ones.