First try at updating the last_compilation date of our bundle.

But it is not enough.
Added ideas in comments.  I like none of those ideas.

src/collective/easyform/profiles/default/registry.xml

@@ -66,7 +66,8 @@
     <value key="compile">False</value>
     <value key="csscompilation">++resource++easyform.css</value>
     <value key="depends">plone</value>
-    <value key="last_compilation">2019-04-24 15:10:00</value>
+    <!-- Please keep this in sync with upgrades.update_last_compilation -->
+    <value key="last_compilation">2020-09-08 17:52:00</value>
     <value key="resources">
     </value>
     <value key="merge_with">default</value>

src/collective/easyform/upgrades/1007.zcml

@@ -13,6 +13,10 @@
         import_steps="actions"
         run_deps="false"
         />
+    <gs:upgradeStep
+        title="Update last_compilation of bundle"
+        handler=".update_last_compilation"
+        />
   </gs:upgradeSteps>
 
 </configure>

src/collective/easyform/upgrades/__init__.py

@@ -0,0 +1,29 @@
+def update_last_compilation(context):
+    # Let's do the imports inline, so they are not needlessly done at startup.
+    # Should not really matter, but oh well.
+    from datetime import datetime
+    from plone.registry.interfaces import IRegistry
+    from zope.component import getUtility
+    from Products.CMFPlone.interfaces import IBundleRegistry
+
+    registry = getUtility(IRegistry)
+    records = registry.forInterface(IBundleRegistry, prefix="plone.bundles/easyform")
+    # Technically we only need year, month and day.
+    # But keep this in sync with registry.xml.
+    records.last_compilation = datetime(2020, 9, 8, 17, 52, 0)
+    # TODO: run the combine-bundles import step or its handler
+    # Products.CMFPlone.resources.exportimport.bundles.combine.
+    # But that only does something when there is a registry.xml,
+    # so I don't think it works for an upgrade step.
+    #
+    # But this is a wrapper around
+    # Products.CMFPlone.resources.browser.combine.combine_bundles
+    # which we could call directly, but then we need to do the same
+    # extra handling of the response contenttype.
+    #
+    # We could also re-apply our whole registry.xml,
+    # by doing an upgradeDepends with plone.app.registry and combine-bundles,
+    # but that restores our factory defaults, which we should not do.
+    #
+    # Easiest is to add an upgrade profile.
+    # I always consider that overkill, but so be it.