The edit field is its own Windows control with its own message loop, so no that won't work.
But this will, if your goal is to hide the edit box:
GUI "Form1", PIXELS
CONST Cmb1_Style = WS_CHILD|WS_VISIBLE|WS_TABSTOP|CBS_HASSTRINGS|CBS_SORT|CBS_DROPDOWN
const ID_Cmb1 = WM_USER + 100
GLOBAL Form1 AS HWND
GLOBAL hCmb1 AS CONTROL
SUB FORMLOAD()
Form1 = BCX_FORM("Form1", 0, 0, 805, 406)
hCmb1 = BCX_COMBOBOX("", Form1, ID_Cmb1, 28, 25, 349, 21, Cmb1_Style)
'============ HIDE EDIT CONTROL ==================
DIM AS HWND hEdit = FindWindowEx(hCmb1, NULL, "Edit", NULL)
IF hEdit THEN HIDE (hEdit)
'============================================
CENTER(Form1)
SHOW(Form1)
END SUB
BEGIN EVENTS
END EVENTS