Hi,
1. I'm afraid that I don't understand your point.
2. You can't have any kind of tag or content which will be replaced by a system plugin.
The checkout modules can be refreshed in Ajax and in that specific way, the Joomla triggers are not called.
So if you want to display your social buttons, best is to add some PHP code to display directly the content.
Otherwise, for plugins, we now have some specific triggers to let others add new fields in the registration form.
3. Yes, that's logical.
4. Please do not edit several times your messages ; it have some very unpleasant and unwanted side effects in our ticket system.
Thank you for your understanding.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.