put your battens on a cooking scale and measure their bending loads, write it on the side of the batten

if the solid glass battens are very close in deflection weight to the foam battens then you can mix them with little change of sail shape

if they are vastly different then you can still mix them but the sail shape will be poor and sail inefficient

which batten did you break on your 5.2?

i broke the number 8 batten on my 5.2. so mixed a little polyester resin up, cut out a couple of bits of glass cloth, stuck it all together and when cured the shape and bend characteristics were almost the same as an unbroken batten

from top to bottom mine were

6.6lb, 3.7lb, 3.7lb, 4lb, 4lb, 3.2lb, 2.8lb, 3.4lb, 3.5lb and 3lb

which is a little strange as they should vary smoothly from top to bottom. think i can swap 7 for 10 but am stuck with 4 and 5

i'll test them all again in the spring when i've finished trying to untwist them and MAY take a little off the top and bottom of the two 4lb battens to soften them up a little

BUT until you measure what you have you won't really get any idea of what you need