I think it should be OK. You could probably use the same concentration as Tween 20. Be careful to avoid using an old, oxidized source of either detergent, which could damage the proteins in your blot.

Thank you so much for your answer Adam

Tween 20 has an HLB of ~16.7, whereas the X-100 is ~13.5.  If it's a formulated buffer (with other additives relying on the Tween to bring them into the water phase), you might be using 1.24 parts of X-100 for every 1 part of Tween 20. 

If this doesn't work in your buffer (if it's not uniform & stable), you'll need a higher HLB Triton X, like X-165 (70%) or X-305 (70%).