This depends on what type of customizations you've made. If you've simply created new files and linked to them from mooSocial, it's unlikely that you will lose any customizations you've made. If you've edited the core code and you overwrite it with the new files from the upgrade package, you may lose your customizations. To avoid this, please make sure you full backup before upgrading, use compare tool to compare and merge changes that you made into the new core code. We do provide upgrading service so that contact us if you’re not sure what you should do.