interesting feature

[WestfW]

  *PFS_P103PFS_BY = 0x05;      // Pulse on D4 to trigger scope 
  *PFS_P103PFS_BY = 0x04;      //  

If you change those to writing a full 32bit word, you can simultaneously force the pin to GPIO (PMR bit) and set the drive strength:

const uint32_t pfsHIGH = (0 << R_PFS_PORT_PIN_PmnPFS_PMR_Pos) |  //GPIO
                         (1 << R_PFS_PORT_PIN_PmnPFS_DSCR_Pos) | // Middle Drive
                         (1 << R_PFS_PORT_PIN_PmnPFS_PDR_Pos) |  // Output
                         (1 << R_PFS_PORT_PIN_PmnPFS_PODR_Pos);   // output High
const uint32_t pfsLOW =  (0 << R_PFS_PORT_PIN_PmnPFS_PMR_Pos) |  //GPIO
                         (1 << R_PFS_PORT_PIN_PmnPFS_DSCR_Pos) | // Middle Drive
                         (1 << R_PFS_PORT_PIN_PmnPFS_PDR_Pos) |  // Output
                         (0 << R_PFS_PORT_PIN_PmnPFS_PODR_Pos);   // output High
//
//    :
//
static inline __attribute__((always_inline)) void dwfast(unsigned int iopin, unsigned int val);
static inline __attribute__((always_inline)) void dwfast(unsigned int iopin, unsigned int val) {
  unsigned int port, bit;
  if (__builtin_constant_p(iopin)) {
    // magic string constants derived from variant.cpp (this for R4 Minima)
    port = "\003\003\001\001\001\001\001\001\003\003\001\001"
           "\001\001\000\000\000\000\001\001\005\000\000\005\005\001\003"[iopin];
    bit = "\001\002\005\004\003\002\006\007\004\003\012\011"
          "\012\013\016\000\001\002\001\000\000\014\015\001\002\010\000"[iopin];
  } else {
    port = iopin >> IOPORT_PRV_PORT_OFFSET;
    bit = iopin & BSP_IO_PRV_8BIT_MASK;
  }
  volatile R_PFS_PORT_PIN_Type *pfs = &R_PFS->PORT[port].PIN[bit];
  if (val) {
    pfs->PmnPFS = pfsHIGH;
  } else {
    pfs->PmnPFS = pfsLOW;
  }
}

const byte myled = 13;

void loop() {
   0:   b508            push    {r3, lr}
    pfs->PmnPFS = pfsHIGH;
   2:   4c08            ldr     r4, [pc, #32]   ; (24 <loop+0x24>)
   4:   f240 4505       movw    r5, #1029       ; 0x405
   8:   6025            str     r5, [r4, #0]
  //  port->POSR = 0x10;

  for (;;) {
#if 1
    dwfast(myled, HIGH);
    delay(300);
   a:   f44f 7096       mov.w   r0, #300        ; 0x12c
   e:   f7ff fffe       bl      0 <delay>
    pfs->PmnPFS = pfsLOW;
  12:   f240 4304       movw    r3, #1028       ; 0x404
  16:   6023            str     r3, [r4, #0]
    dwfast(myled, LOW);
    delay(300);
  18:   f44f 7096       mov.w   r0, #300        ; 0x12c
  1c:   f7ff fffe       bl      0 <delay>
  20:   e7f2            b.n     8 <loop+0x8>
  22:   bf00            nop
  24:   4004086c        .word   0x4004086c