def alterModelDef(dbTuple, name=None, format=None, dbType=None, single=None,
                  official=None, numver=None, purgeAge=None):
    """Alter GFE database definition. The definition is used in the dbs setting
    and has form:
                     (name,  format,  type, single, official, numVer, purgeAge)
    i.e., Practice = ("Fcst",  GRID, "Prac",   YES,       NO,      1,   24)

    Won't use these exact names since some might conflict with builtins
    Only supply what you want to change. To clone a model definition, just
    supply name='newname'
    """
    n,f,t,s,o,v,p=dbTuple
    l=[]
    for old,new in [(n,name),(f,format),(t,dbType),(s,single),(o,official),
                    (v,numver),(p,purgeAge)]:
        if new is None:
            l.append(old)
        else:
            l.append(new)
    return tuple(l)