Try
list //. {bef,PatternSequence[x, m] /;StringQ[m] && StringFreeQ[m, DigitCharacter], aft} :> {bef, LIST[x, m], aft} /. LIST -> List
How about this:
lines //. {bef___, x_String, m_String /; StringFreeQ[m, DigitCharacter], aft___} :> {bef, temp[x, m], aft} /. temp -> List