Microsoft Access 掲示板

標準モジュールに以下を定義すると、

Function f_strInsAfter(strOrg As String, strBgn As String, strEnd As String, strIns As String) As String
    Dim p1 As Long
    Dim p2 As Long
    
    p1 = InStr(strOrg, strBgn)
    If p1 = 0 Then
        f_strInsAfter = strOrg
        Exit Function
    End If
    
    p2 = InStr(p1, strOrg, strEnd)
    If p2 = 0 Then
        f_strInsAfter = strOrg
        Exit Function
    End If
    
    If Len(strOrg) < (p2 + Len(strEnd)) Then
        f_strInsAfter = Left(strOrg, p2 + Len(strEnd) - 1) & strIns
    Else
        f_strInsAfter = Left(strOrg, p2 + Len(strEnd) - 1) & strIns & f_strInsAfter(Mid(strOrg, p2 + Len(strEnd)), strBgn, strEnd, strIns)
    End If
    
    
End Function

f_strInsAfter([説明文],"＜img","＞","＜br＞")
がご所望の文字列を返します。