Here is one of mine and yes, it can be conditioned... but you conditional the update of the Attribute rather than the conditioning the css.
However...... If you have two css classes named, say myclassYes and myclassNo and then you have a Yes/No attribute then your can pick up a different class depending on the value of the attribute... if you know what I mean.
If ProjectSummary.SummaryLevel<>'AREA' Then
ProjectSummary.Finance_OriginalBudgethtml=<a href=
+SystemSettings.CharQuote+#
+SystemSettings.CharQuote+class=
+SystemSettings.CharQuote+ProjectSummary.SummaryLevel+SystemSettings.CharQuote+onClick=
+SystemSettings.CharQuote+AwareApp.startProcess2('VIEWOriginalBudget','ProjectSummary',
+ProjectSummary.ID+,'new_tab')
+SystemSettings.CharQuote+>
+AS_STRING(ProjectSummary.Finance_OriginalBudget,'#,###;(#,###)')+</a>
ELSE
ProjectSummary.Finance_OriginalBudgethtml=<a href=
+SystemSettings.CharQuote+#
+SystemSettings.CharQuote+class=
+SystemSettings.CharQuote+ProjectSummary.SummaryLevel+aw-decorated-grid-cell
+SystemSettings.CharQuote+onClick=
+SystemSettings.CharQuote+AwareApp.startProcess2('VIEWOriginalBudget','ProjectSummary',
+ProjectSummary.ID+,'new_tab')
+SystemSettings.CharQuote+>
+AS_STRING(ProjectSummary.Finance_OriginalBudget,'#,###;(#,###)')+</a>