If you manually rename the DSL File ( DSLDefinition.dsl ) to something else you will notice that your project will not work anymore giving several weird error messages.
The Solution is to manually also change all the .tt files that are still referencing the old name.
Default Name : DslDefinition.dsl
Search for this name and you will find that all the .tt files are still referencing the old name.
<#@ Dsl processor="DslDirectiveProcessor" requires="fileName='..\DslDefinition.dsl'" #>
<#@ include file="Dsl\ConnectionBuilder.tt" #>