Add Exchange attributes to ActiveDirectory

Hello,

I would like to extend my Active Directory schema for Office 365.

I need to modify the attribute msExchHideFromAddressLists, but I use my local AD to synchronize to Office 365 with AADConnect, and I never had Exchange on-premise server.

I found some discussions like this one : https://answers.microsoft.com/en-us/msoffice/forum/msoffice_o365admin-mso_dirservices/how-can-i-add-this-msexchhidefromaddresslists/5043d1ce-b7eb-45f7-8848-c07245ad8e66 or this one : https://techcommunity.microsoft.com/t5/Office-365/Adding-Exchange-Attributes/m-p/187420#M12580.

But I don't want to take any risks in doing so. What is the danger of doing this?

Is the update schema in AADConnect is long?

I'm a little bit afraid to extend my schema and that nothing work after that.