▪Basically, we use the edit tool , transform tool , copy/paste Properties tool to do all the editing.
 

▪Transform Items

You could move the item, set up the its size in attribute editor,

beside that, you use the transform tool to transform buttons size & position, the hotkey for this tool is "CTRL + T".

Select picker items, enter this tool to transform them, press Enter/Return key to confirm the transformation, Escape key to cancel the transformation.

Use "ALT + Enter/Return" to apply the mirrored transformation to the mirrored items.

▪Transform Bezier / Polygon Shape:

You could rotate / flip bezier curve and polygon shapes, just go to Edit Menu / Transform Bezier/Polygon Item..

▪Duplicate Items

Select a picker item, press "CTRL + D" to duplicate them and position the duplications below them.

"CTRL + SHIFT + D" to duplicate and position the duplications to the right side of them.

Holding ALT key while doing this, will position the duplications to the opposite side, say the left or top side of the original items.
 

▪Copy / Paste Items

CTRL + C / CTRL + V also works for the select items.

You could copy items and paste them into other picker files.

When copying items, if picker panels are selected, only panels will be copied, other type of items are skipped.
 

▪Copy / Paste Item Properties

Switch to copy/paste property tool , to transfer the properties between picker items. use hotkey "I" for that.

To copy the properties, right click on the item, select a copy mode.

LMB click on item to paste the properties.
 

▪Align / Evenly Distribute Items

Use the align/distribute buttons in the ui, or the corresponding menus in the Edit menu, to align / evenly distribute selected picker items.
 

▪Scale Item to Proper Size

Select picker item, press "CTRL + R" to rescale them to its proper size. Same feature available in the Edit menu.
 

▪Adjust Item Fill Color

You could adjust the items color in attribute editor.

But if you wanna tweak the color in photoshop way:

Select picker item, press "CTRL + U" to bring up the "Adjust Button Color" dialog.

It is very similar to photoshop's "Hue & Saturation" dialog.
 

▪Set Properties To Mirrored Item

Use ALT key.

Say setting the label margin, input the label margin and press ALT+Enter, the mirrored item will be applied the mirrored label margin.

Say you are transforming items using transform tool, user ALT+Enter, to apply the mirrored transformation to the mirrored items.
 

▪Parent / Unparent Item

All types of picker items, including picker panel itself, could be parented into a picker panel.

By default when you create a picker item upon a picker panel, the item will automatically be the child item of the panel below.

To parent items to a panel, select and move the items over the panel, make sure your are in tool, right click and select "Parent To Panel Below".

The same way, if you wanna unparent items from a panel, select them, right click and select "Unparent From Parent Panel";
 

▪Auto-Label Item

Select picker item, press "CTRL + L" to auto-label them.

An alternative way, press the < button beside the label field in attribute editor.

▪Change the Item Stack Order

Select picker item, press "CTRL + Up key" to bring them to top stack order, "CTRL + Dn key".to push them down to the bottom stack.

Picker panel is always the bottom stack order, and tend to be covered by other type of picker items.

▪Editing an Existing Image

There are several image properties for picker item, such as background image for panel, item image for select-button, command-button and slider handle.

At the attribute editor, at the right side of each image path field, there is a > button, click and select "Edit image.." to bring up the image processing dialog.

▪Auto-Set a Proper Post Action for Select-Buttons:

Post action are the behaviors after mouse click on a select-button in animator mode, you can set to auto-switch to translate tool, rotate or scale tool or just do nothing.

A proper post action will save time for animator.

To auto-set the proper action for selected select-buttons, go to Edit Menu / Auto-Set Sel-Button Post-Actions.

It will test member nodes of each select-button, say if the nodes are all locked in rotate and scale attributes, it will set post action to "Switch to Translate".