You are correct in transferring your count title will give the entire stack over to them, it is how the system is intended to work. If you wish to keep your mayor title, then you must wait until after Domain & Settlement Selection to will the title over to them. However, using this method will result in having the county seperate from your reciever of the title, and it will not be merged into their county.
From "Account merging is almost here!"
Transfer All Titles & Lands
If you have a package but wish to give a set your titles and lands to another player, there will be an opportunity to do so before Settlement & Domain Selection. This does not occur prior to Merging.
Here's what would happen when that time comes:
• A Title Bundle would transfer to the new account, along with whatever rewards go along with that title (full stack of titles, lands, cloaks, surname & crests, etc). If you have another stack of titles left, those remain on your account.
• Your Total Influence will stay the same since you still paid for it.
• You retain all other package rewards (launch party tickets, sparks of life, design experiences, etc).Note: This is not the same as willing one of your titles to another player. Willing a title to another is done after Settlement & Domain Selection and you will still be responsible for picking your domain and/or settlement before willing them to another.
For example, if you want to have a county but give a friend your duchy, you'll do this after you've selected the lands.
From Caspian on Discord regarding transferring (11-1-17) (right-click for a bigger image):
Title Stack Transfers (02-13-18) (right-click for a bigger image):
Caspian on Willing Titles (02-24-17):
3). Willing. Because not everyone wants to play all of their titles, we're giving people the ability to will away their titles to other. This is something that can be done after domain / settlement selection. The person who owns the title chain will participate in domain / settlement selection, will pick their settlements and any domains, and then can, at their discretion give some or all of their titles over to other people. In doing so they forfeit all rights to the titles they held.
Note that this does not transfer EP, Influence, or anything else. It simply grants someone else the title and the ability to manage the settlement / domain. Think of it as though it were willing your domain / settlement to someone post-launch. It just happens now instead of post-launch so they can begin managing their domain / settlement immediately.