Those who have used the AecColumnGridLabel command (COLUMNGRIDLABEL also works; on the Column Grid contextual ribbon tab, on the Label panel, the Label tool) to add grid bubbles to a "standard" Column Grid object will recall that there are radio buttons on both the X-Labeling and Y-Labeling tabs to choose either an Ascending or Descending order for the labels.
For Custom Column Grids created by converting linework, the AecCustomColumnGridLabelAdd and AecCustomColumnGridLabelEdit commands (CUSTOMCOLUMNGRIDLABELADD and CUSTOMCOLUMNGRIDLABELEDIT; on the Column Grid contextual ribbon tab, on the Label panel, the Add Labels and Edit Labels tools) allow you to select one or more of the custom grids and add/edit grid bubbles. When more than one grid is selected, an increasing sequence of label values is generated, based on the order the grid were selected, so you can control the ordering when selecting the grid lines.
Control over the ordering of grid labels when creating or editing Enhanced Custom Column Grids is also possible. You could place the grid and then use the same commands/tools noted above for Custom Column Grids, but that would not allow you to take advantage of the automatic secondary label formatting available with the enhanced custom grid. The good news is that you can control the ordering of the labels either when initially creating an Enhanced Custom Column Grid (AecCustomColumnGrid or CUSTOMCOLUMNGRID; on the Home ribbon tab, on the Build panel, the Enhanced Custom Grid tool) or editing one (AecCustomColumnGridEdit or CUSTOMCOLUMNGRIDEDIT; on the Column Grid contextual ribbon tab, on the Custom Grid panel, the Edit Grid tool). Either of these actions opens the Column Grid dialog.
The bad news is the location of where you would indicate whether you want an ascending (the initial default) or descending order is not immediately obvious, as it is in the Column Grid Labeling Dialog for standard Column Grids. What you need to do is select the X-Labeling and/or Y-Labeling drop-down lists in the Bubble Parameters area, Label Format sub-area, and choose the Custom: ZZZ option, where ZZZ is a varying string indicating the currently selected labeling options. As shown in the image below, the Custom Label dialog that appears after making that selection allows you to choose the ordering (Left to Right or Right to Left for the X-Labeling and Bottom to Top or Top to bottom for the Y-labeling).