whell. making it call another skin would result in a slow time of response. but if you create more entrys of items in the skins and in the variables files you could add more launchers, and say you want to make this new launchers apear when you click one of the originals items.
what you have to do to make this is make a group with your new launchers, and make it so when you click one of the originals items it shows the sub-launchers, and when your mouse leaves the skin deseapears as the rest of the skin
i'll try to explain it better
as you can se in the skin, every launcher icon has in their options an entry call Group=1 as well as an entry "hidden=1"
the hidden is so they don't show by default.
and then the arrow has this entry: MouseOverAction=!Execute [!RainmetershowMeterGroup 1][!RainmeterRedraw]
that makes it show the entire group 1
and finally the backgroud entry has a command similar to this last one but instead of showing the icons it hides them when your mouse leave the area of the skin
if you follow me until now you might have an idea of what you have to do.
you create 10 more icons entry from 11 to 20 , as whell as the variables in the variables file and the entrys for the apps titles as well, then to the icons entrys you made, make them be a group 2 instead of 1
and put this "LeftMouseUpAction=!Execute [!RainmetershowMeterGroup 2][!RainmeterRedraw]" whitout quotes in the variable of the icon you want to use to show the other ten.
and finally modify the background command so that it looks like this
MouseLeaveAction=!Execute [!RainmeterhideMeterGroup 1][!RainmeterhideMeterGroup 2][!RainmeterhideMeter Arrowhover][!RainmetershowMeter Arrow][!RainmeterRedraw]
so that when your mouse leave the skin the group 2 desapears as well
remember to put well the names of the new entrys you create, the entrys for the text, and the variables in the variables file don't repeat any number.
i hope you can understand and that i had been able to help you. let me know how it goes!!