Change URL structure of forum

Hello Everyone, We make use of a SMF (Simple Machines) Forum. We also use the Pretty URL Mod. But we want to change the URL slug of the TOPICS for just 1 category. All topics in the category/board: "Wasdroger kapot en repareren" Look Like: DOMAINNAME/BOARDNAME/TOPICNAME/ But only for topics (current and future topics) in this board we want to show the URL's as: DOMAINNAME/TOPICNAME/ So without the boardname. Keep in mind this modification may not malfunction the forum in any way. Also it must not change any available functions. After it is OK we want to know exactly what you did to archieve this. Because we want to duplicate it to another board of us also and we want to know how to undo the changes when we want to. SO we would like to receive a document with detailed description for this. Please make your bid. Kind regards, Jarno