So here is th esolution for Loop Mode :
<action name="beatspotsOn">
delayedcall(5.0,tween(layer[glaceannou].scale, 1.2, 0.5, default, tween(layer[glaceannou].scale, 1, 0.5, default, beatspotsOn() ) ));
</action>
<layer name="glaceannou" url="images/glaceannou.png" align="topleft" x="10" y="10" tooltip="Intégrez votre Mascotte" keep="true" onclick="flyin(zoom-mascotte);" onover="tween(alpha,0.5);" onout="tween(alpha,1.0);" />
The layer animation will start after 5 secondes.
The layer is scalling from 100% to 120% for 1seconde, then the layer is scalling down from 120% to 100% for 1seconde.
The animation is looping !!!
Hope it could help some of you !