Since erp5@6c6b77a0, this is now a safe operation, in that a mistake while moving databases won't result in a loss of the catalog if the zodb is empty.

This new implementation relies on erp5@6bb4c56e, which means that zopes decide on their own to create the site at startup if there's none, and the 'erp5-bootstrap' service is removed from the root partition.

Contrary to what was planned, it remains possible to list several bt5 to install. In itself, it's trivial to restrict to a single bt5, to prevent people from overusing this feature:

--- a/product/ERP5/ERP5Site.py
+++ b/product/ERP5/ERP5Site.py
@@ -1889,7 +1889,7 @@ def create(self,
         bt5_repository_url.split())
       if bt5:
         p.portal_templates.activate(after_method_id="immediateReindexObject",
-          ).upgradeSite(bt5.split(), update_catalog=True)
+          ).upgradeSite([bt5], update_catalog=True)
 
     return p
 
--- a/product/ERP5/dtml/addERP5Site.dtml
+++ b/product/ERP5/dtml/addERP5Site.dtml
@@ -110,7 +110,7 @@ label {
 
   <fieldset>
     <legend class="form-title">Business Templates</legend>
-    <div title="Business Template names, or (TODO) URL pointing to a file in BT5 or ZEXP format.">
+    <div title="Business Template name, or (TODO) URL pointing to a file in BT5 or ZEXP format.">
       <label class="form-label" for="bt5">Install BT5</label>
       <input class="form-element" name="bt5" id="bt5" type="text" size="60"/>
     </div>

However, applying it now would break the default behaviour, which consists in installing many configurators, plus erp5_data_notebook in the case of wendelin. This must be done in a separate commit, after a review of BT dependencies.