🚀 go-pugleaf

If the design calls for 25 ohm coax, you  will probably need 25 ohm 
coax!  I know of several designs where the coax  is used as a balun or
a transformer, or an impedance multiplier.  It may also be used as
a matching element in an impedance transform.  

     I don't think two 50 coax lines will work, as any mismatch in 
length or velocity factor can set up a "cavity" mode (actually, 
a shorted transmission line or "re-entrant" transmission line resonator)
which can cause serious in band "suck-outs".
This is especially true if the length of coax is approaching a significant
(> 1/8) portion of a wavelength of the operating frequency.

Joeld.

PS.  What is the circuit?