X-men powers Q&A

[eluvium]

Can Armor's exoconstruct change size?

[UnkoMan]

"In instances of extreme duress, Hisako is also able to expand her armor, greatly strengthening and increasing its size and shape around her...in Astonishing X-Men vol. 3 #39, Armor's armor expands and grows to the size of a building due to the fact she feels strongly about not attending her recently deceased mother and brother's wake."

That's from wikipedia. It appears the answer is yes, under certain circumstances.