How to derive an exact 10Hz clock from the generated clock?
Here's one way: count to 5 million and then toggle a flip flop.  If timing is an issue in your part, you can pre-divide down to a lower frequency first (divide by 4, for example), then count to 1.25 million in your secondary counter.
reg [22:0] main_counter;
reg        clock_10hz;

wire       toggle;

assign  toggle = (main_counter == 23'd4_999_999);  // 5e6 including 0.

initial begin
   main_counter = 0;
   clock_10hz   = 0;
end

always @(posedge clock_100m)
    if (toggle) begin
         main_counter &lt;= 0;
         clock_10hz   &lt;= !clock_10hz;
    end
    else begin
         main_counter &lt;= main_counter + 1;
    end

Update: edited counter to 5 million (was 50 million).  OP asking for 10Hz, not 1Hz.