So now Pedag Balances have been ordered and arrived. And gosh, there's very little room in skates to stick a hand down and make minute adjustments.
Attempts to use stick in velcro unsuccessful so far, lots of fiddling resulted in the bottom layer removing the top surface of the hardboardy bit under the insole.
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In the end I positioned the right one just by nestling it where it fitted the boot and slapping on some sellotape.
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Yeah, it's difficult to adjust the positions of the arch supports while they are inside the boots. Here's what I do. I remove the insoles from the boots. After I attach the arch supports (Steps for me) to the insoles [see below], I use a fine color marker (first color) to trace the outlines of the arch supports on the insoles. I then insert the insoles into the boots and try them on to see how they feel. I get an initial estimate of whether they need to be repositioned. If they do need to be repositioned, I remove the insoles from the boots again, and remove the arch supports from the insoles again. Using the previously traced outlines as guides, I reposition and reattach the arch supports. I then retrace the outlines of the arch supports on the insoles with a fine color marker (second color). Repeat as needed. You can do a couple of iterations off-ice; attach blade guards to your blades, stand and walk about the floor. Do final adjustments after you skate on them.
Here's a tip for dealing with Velcro tape. Remove the double-sided sticky tape from the bottoms of the arch supports. Line the entire bottom surfaces of the arch supports with the hard Velcro. Trim the Velcro with sharp scissors to conform to the bottom surfaces of the arch supports.
Now, line regions of the top surfaces of the insoles with soft Velcro. The areas of the soft Velcro should exceed the areas of the bottoms of the arch supports over their target positions (allow a minimum of ~2 cm excess all around). If you think you have sufficient clearance in the toe and heel regions, I would simply cover the entire top surfaces of the insoles with soft Velcro (makes a good surface to plant your foot on). [See below for moleskin interface.] Again, trim the Velcro to conform to the insoles.
If you need to reposition the arch supports, to avoid tearing the top surfaces of the insoles, don't yank the arch supports off. Use your thumb and forefinger of one hand to hold down a portion of the hard Velcro and insole adjacent to a portion of the arch support. With your other hand, slip a fingernail under the adjacent portion of the arch support, and slowly start to "peel" the arch support from the insole. Once you have enough clearance, grab the arch support with your thumb and forefinger, and peel the insole and arch support away from one another until they are completely separated.
If you want a smoother, less abrupt, feel to the arch supports, cover the top surfaces with soft Velcro if you have sufficient clearance. Otherwise cover with moleskin. Note: If you want to play it safe, use moleskin first. You can then cover the moleskin with soft Velcro. If you apply Velcro tape directly to the top leather of the arch support, and then decide to remove the Velcro, you could damage the leather surface (the Velcro adhesive is very sticky). The adhesive on the Curad moleskin is less sticky (even so, if you need to remove the moleskin, peel it away slowly to avoid tearing the leather surface; don't yank). [You can use this same moleskin interface if you're concerned about damaging the top surfaces of the insoles if you need to remove Velcro tape from the insoles.]
You don't want to depend on sticky tape to hold the arch supports in place. They will come loose after a while, and your boots will feel different.
Good luck!