Replacement of some tags in web.config in a section

Question

I want to replace some tags from appsettings section but not all of them, and I don't want to write

xdt:Transform="SetAttributes" xdt:Locator="Match(key)"

for all of them, is there any pattern matching available so I can transform all the ones that start with a certain prefix. Example

<appsettings>
    <add key="a" value="a" />
    <add key="r_a" value="X" />
    <add key="r_b" value="B" />
</appsettings>

and use a transform that replaces the ones starting with _r at the appsettings level?

Haven't found anything yet.