To pause specific sessions,  using FiddlerScript to the OnBeforeRequest function (except where noted). For example:

Pause all HTTP POSTs to allow hand-editing (the POST verb is often used for submitting forms)

if (oSession.HTTPMethodIs("POST")){ oSession["x-breakrequest"]="breaking for POST"; }

Pause all HTTP POSTs that contain 'thekeyword'

if (oSession.HTTPMethodIs("POST") && (oSession.utilFindInRequest("thekeyword", true) > -1)){ oSession["x-breakrequest"] = "keyword"; }

Pause a request for an XML file to allow hand-editing

if (oSession.url.toLowerCase().indexOf(".xml")>-1){ oSession["x-breakrequest"]="reason_XML"; }

Pause a response containing JavaScript to allow hand-editing (in OnBeforeResponse)

if (oSession.oResponse.headers.ExistsAndContains("Content-Type", "javascript")){ oSession["x-breakresponse"]="reason is JScript"; }