YES YES YES!!!!!!
I don't know that anyone cares but me, but this MADE MY DAY!!!
I wrote D'Addario and asked them this;
"I am a cellist and I like to compose for strings in my spare time. In my current little diddy, I would like to use a fair bit of scordatura, but am unsure how much cello strings can take! (Or any bowed string, for that mattter.) Can I tune an A string up to a C natural and play on it without harming it? Would it make a difference if I was only playing it open, not putting any fingers down? Would it make more sense to use a string designed for a 3/4 size cello? If not, do you design any such strings that would permit me to do this? If you have the time, I would be interested in all the different bowed strings. I thank you in advance for your time and consideration."
They replied:
"The relationship between frequency, tension and mass per unit length of a vibrating string is:
Freq = [1/(2 x Length)] x squareroot(Tension/UnitMass)
If you use the same string and keep the open string playing length the same, but tune it to a different frequency, then the tension varies as the square of the frequency (unit mass is unchanged). A semitone is about 6% change in frequency, so if you tune a string up by a semitone, the tension increases by about 1.06^2 or about 12%. Tune it up a whole tone and the tension increases by 1.06^4 or about 26%. Etc. So you can see the tension goes up very quickly as you tune up the string.
The breaking point of a string depends on the properties and size of the core. The upper strings have less breaking margin since they are designed with higher playing tensions AND have thinner cores.
So tuning up strings by a whole tone should not result in breaking problems except for the A string (which operate with less margin). The bottom strings can probably be tuned up by a third without breaking. However, even if they don’t break, with their higher tensions, the strings will sound and respond very differently (and different than adjacent strings that are not tuned up). Some scordatura tunings deliberating (I think they meant "deliberately") take advantage of these differences, but in other cases, the mismatches are problematic.
It makes no difference if you put a finger down (that changes the vibrating length and frequency, but not the tension). A 3/4 size string is worse (for tuning up, but better for tuning down), since it is designed with more mass, so its playing tension at full size is actually higher than a 4/4 size string. A light tension string will help, but only by about 10%.
For guitar strings, we manufacture strings in a complete range of diameters which makes it easier to pick strings for non-standard guitar tunings. However, for bowed instruments, we make strings only for standard tunings, so picking strings for non-standard tunings may not be possible without custom designed strings.
All of our playing tensions are in our website. I hope this information is helpful. Good luck!"
P.S.- I'm gonna do it... but I may skip the high C natural when I do.