If make DF to 1, can I confirm that fragmented packet with DF=1 will go through routers to the dest IP without any reassembly and re-fragmentation?
Interesting question. The DF bit is usually only set by the source, but it's technically possible for any hop to set it, even after fragmentation.
RFC 791 states (emphasis mine)
An internet datagram can be marked "don't fragment." Any internet datagram so marked is not to be internet fragmented under any circumstances. If internet datagram marked don't fragment cannot be delivered to its destination without fragmenting it, it is to be discarded instead.
If the Don't Fragment flag (DF) bit is set, then internet fragmentation of this datagram is NOT permitted, although it may be discarded.
That very closely makes fragments (MF bit set or fragment offset > 0, and identification filled) with a set DF bit illegal and may cause them to be dropped right away.