How to update field of ReadOnly Child Using Relationship Name

HI Guys,

The scenario is as follows:-

<b>Parent</b> (Has Read Read/ Write BDoc Specified)- But Does not has the Segment Field that is to be modified

<b>Relationship Name</b> Is specified b/w Parent and Child

<b>Child</b> (Has only Read BDoc Specified)- Has the segment field that is to be modified.

<b>BQuery</b> - Exists for the parent BDoc

Is it possible to update the field in child BDoc by any means..?????

Directly or Indrectly?

Please help with Syntax.

Thank You in advance