Can I configure multiple plugin executions in pluginManagement, and choose from them in my child POM?

You’re correct, by default Maven will include all of the executions you have configured. Here’s how I’ve dealt with that situation before.

<pluginManagement>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>some-maven-plugin</artifactId>
    <version>1.0</version>
    <executions>
      <execution>
        <id>first-execution</id>
        <phase>none</phase>
        <goals>
           <goal>some-goal</goal>
        </goals>
        <configuration>
          <!-- plugin config to share -->
        </configuration>
      </execution>
      <execution>
        <id>second-execution</id>
        <phase>none</phase>
        <goals>
           <goal>other-goal</goal>
        </goals>
        <configuration>
          <!-- plugin config to share -->
        </configuration>
      </execution>
    </executions>
  </plugin>
</pluginManagement>

Note, the executions are bound to phase none. In the child, you enable the parts that should execute like this:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>some-maven-plugin</artifactId>
    <executions>
      <execution>
        <id>first-execution</id>         <!-- be sure to use ID from parent -->
        <phase>prepare-package</phase>   <!-- whatever phase is desired -->
      </execution>
      <!-- enable other executions here - or don't -->
    </executions>
</plugin>

If the child doesn’t explicitly bind the execution to a phase, it won’t run. This allows you to pick and choose the executions desired.