Garden Fence - Can I change my fence without the developers permission? ?

Sure you can,

Just as they can insist that you change it back.

Emails are not a recognised form of communication.  Use recorded delivery.

You should check with your county zoning office or housing office to see if permission is needed. If you own the property and there is no 'condo' association or housing association associated with the property--one that would regulate the height and type of fencing--then I don't see why you can't replace the fence you have with another one. If the developers own the property where the fence is, you're simply not going to be able to change that. NEVER proceed without the proper permitting and permissions when it comes to an expensive change to your home or property. You can really get into trouble, and it will end up costing you a lot. 

If you have a deed restriction and do otherwise they could require you to tear any changes down.

Deed says you need permission, you need permission.

It is common for a developer to require approval in a new development, but it is equally common for the developer to pass the power of approval to the newly formed home owners association.  Talk to your neighbors to see if one exists and or if they have alternative methods to contact the developer.  Building without approval (or a county building permit) will risk you having to take it down if it doesn't meet approval.

Apparently not, if thats what the title deed says.  Have other people changed thiers?  If you did this anyhow and gave the old "poop pitiful me, I didn't know I couldn't do that" then they may just let it go but more likely they'll make you change it back.

If you have deed restriction they are legal and so the answer is no

Send the a letter, registered, stating your intentions and that if you receive no replay within 30 days of your letter it will be interrupted and their approval of the project.   It's not going to hold up in court as a legal approval, but it will probably force them to at least contact you.  

Obviously the answer to your question is "no."   You live in a deed restricted area.