Modifying Squares

[TikiPrincess]

How can I modify other patterns to match the guage and size?
I'm working with Joanne Clark's Tech Square Afghan to make a sampler as my cousin's wedding present, but I don't like some of the blocks and I want to add a few more to make it wider. I know I can repeat some of the patterns, but I wanted to try to make different squares.
Desired Size and Requirements:
Yarn: Worsted Weight
Needle: US 7
Gauge: 18 sts = 4"
Finished size = approx. 13" x 13"

I borrowed 200 Knitted Blocks by Jan Eaton. It uses US 6 needles for a 6" square with DK yarn. Is there a general way to convert the blocks to my requirements? Or do I need to post the individual patterns?

I've only completed two of the tech squares, so it's not too late to change to something else, but I kinda like the big squares because it means I get to practice the technique longer.

[Abbily]

I've never done a pieced afghan, but it seems to me that your gauge wouldn't matter between squares, as long as they come out to the same size so you can seam them together.

[megan734]

It basically shows that you have NO problem. If you GRAFT the sqares you can check out other websites to show you if you are saying, IDK. Good luck!