On my first sweet fixie I un-carefully, heavy handedly splayed a pearl (25.4) to 26.4 without realising what I was doing, and it was fine, for about a year and a half, but cracked at a later date possibly when removing the bars...
I would guess that carefully, very gently, easing a 26 bar into a nitto 25.4 would possibly be alright.
Others will contradict me I'm sure, but I just speak from experience.
On my first sweet fixie I un-carefully, heavy handedly splayed a pearl (25.4) to 26.4 without realising what I was doing, and it was fine, for about a year and a half, but cracked at a later date possibly when removing the bars...
I would guess that carefully, very gently, easing a 26 bar into a nitto 25.4 would possibly be alright.
Others will contradict me I'm sure, but I just speak from experience.