올려주신 내용처럼 카테고리 계층형을 변경하시려면

wp-content/plugins/kboard/skin/사용중인 스킨/list-category-tree-tab.php 파일 중 아래 코드 부분을

		<div class="kboard-tree-category-wrap">
			<?php $tree_category_list = $board->tree_category->getCategoryItemList()?>
			<div class="kboard-search-option-wrap-<?php echo $board->tree_category->depth?> kboard-search-option-wrap type-tab">
				<input type="hidden" name="kboard_search_option[tree_category_<?php echo $board->tree_category->depth?>][key]" value="tree_category_<?php echo $board->tree_category->depth?>">
				<input type="hidden" name="kboard_search_option[tree_category_<?php echo $board->tree_category->depth?>][value]" value="<?php echo $board->tree_category->getCategoryNameWithDepth($board->tree_category->depth)?>">
				<ul class="kboard-tree-category">
					<li<?php if(!$board->tree_category->getCategoryNameWithDepth($board->tree_category->depth)):?> class="kboard-category-selected"<?php endif?>><a href="#" onclick="return kboard_tree_category_search('<?php echo $board->tree_category->depth?>', '')"><?php echo __('All', 'kboard')?></a></li>
					<?php foreach($tree_category_list as $item):?>
					<li<?php if($board->tree_category->getCategoryNameWithDepth($board->tree_category->depth) == $item['category_name']):?> class="kboard-category-selected"<?php endif?>><a href="#" onclick="return kboard_tree_category_search('<?php echo $board->tree_category->depth?>', '<?php echo $item['category_name']?>')"><?php echo $item['category_name']?></a></li>
					<?php endforeach?>
				</ul>
			</div>
			
			<?php foreach($board->tree_category->getSelectedList() as $key=>$category_name):?>
				<?php $tree_category_list = $board->tree_category->getCategoryItemList($category_name)?>
				<?php if($tree_category_list):?>
				<div class="kboard-search-option-wrap-<?php echo $board->tree_category->depth?> kboard-search-option-wrap type-tab">
					<input type="hidden" name="kboard_search_option[tree_category_<?php echo $board->tree_category->depth?>][key]" value="tree_category_<?php echo $board->tree_category->depth?>">
					<input type="hidden" name="kboard_search_option[tree_category_<?php echo $board->tree_category->depth?>][value]" value="<?php echo $board->tree_category->getCategoryNameWithDepth($board->tree_category->depth)?>">
					<ul class="kboard-tree-category">
						<li<?php if(!$board->tree_category->getCategoryNameWithDepth($board->tree_category->depth)):?> class="kboard-category-selected"<?php endif?>><a href="#" onclick="return kboard_tree_category_search('<?php echo $board->tree_category->depth?>', '')"><?php echo __('All', 'kboard')?></a></li>
						<?php foreach($tree_category_list as $item):?>
						<li<?php if($board->tree_category->getCategoryNameWithDepth($board->tree_category->depth) == $item['category_name']):?> class="kboard-category-selected"<?php endif?>><a href="#" onclick="return kboard_tree_category_search('<?php echo $board->tree_category->depth?>', '<?php echo $item['category_name']?>')"><?php echo $item['category_name']?></a></li>
						<?php endforeach?>
					</ul>
				</div>
				<?php endif?>
			<?php endforeach?>
		</div>

아래 코드로 변경해보시겠어요?

		<div class="kboard-tree-category-wrap">
			<?php $tree_category_list = $board->tree_category->getCategoryItemList()?>
			<div class="kboard-search-option-wrap-<?php echo $board->tree_category->depth?> kboard-search-option-wrap type-tab">
				<input type="hidden" name="kboard_search_option[tree_category_1][key]" value="tree_category_1">
				<input type="hidden" name="kboard_search_option[tree_category_1][value]" value="<?php echo $board->tree_category->getCategoryNameWithDepth('1')?>">
				<ul class="kboard-tree-category">
					<li <?php if(!$board->tree_category->getCategoryNameWithDepth($board->tree_category->depth)):?> class="kboard-category-selected"<?php endif?>><a href="#" onclick="return kboard_tree_category_search('<?php echo $board->tree_category->depth?>', '')"><?php echo __('All', 'kboard')?></a></li>
					<?php foreach($tree_category_list as $item):?>
					<li <?php if($board->tree_category->getCategoryNameWithDepth('1') == $item['category_name']):?> class="kboard-category-selected"<?php endif?>>
						<a href="#" onclick="return kboard_tree_category_search('1', '<?php echo $item['category_name']?>')"><?php echo $item['category_name']?></a>

						<?php foreach($board->tree_category->getSelectedList() as $key=>$category_name):?>
							<?php $tree_category_list = $board->tree_category->getCategoryItemList($category_name)?>
							<?php if($tree_category_list && $category_name == $item['category_name']):?>
							<div class="kboard-search-option-wrap-<?php echo $board->tree_category->depth?> kboard-search-option-wrap type-tab">
								<input type="hidden" name="kboard_search_option[tree_category_2][key]" value="tree_category_2">
								<input type="hidden" name="kboard_search_option[tree_category_2][value]" value="<?php echo $board->tree_category->getCategoryNameWithDepth('2')?>">
								<ul class="kboard-tree-category">
									<?php foreach($tree_category_list as $item):?>
									<li <?php if($board->tree_category->getCategoryNameWithDepth('2') == $item['category_name']):?> class="kboard-category-selected"<?php endif?>>
										<a href="#" onclick="return kboard_tree_category_search('<?php echo $board->tree_category->depth?>', '<?php echo $item['category_name']?>')"><?php echo $item['category_name']?></a>
									</li>
									<?php endforeach?>
								</ul>
							</div>
							<?php endif?>
						<?php endforeach?>
					</li>
					<?php endforeach?>
				</ul>
			</div>
		</div>

위 코드는 1단 2단까지만 출력되도록 구성되어 있습니다. 

이후 카테고리의 CSS는 적절히 조정하셔서 사용하시면 될 듯 합니다.

카테고리별 게시글 수는 아래 링크를 참고해주시겠어요?

https://www.cosmosfarm.com/threads/document/13544

고맙습니다.